diff --git a/tests/test_base64.cpp b/tests/test_base64.cpp
index c95e3c9..6f80acf 100644
--- a/tests/test_base64.cpp
+++ b/tests/test_base64.cpp
@@ -14,7 +14,7 @@ std::size_t input_length = sizeof(input) - 1;
 std::size_t output_length = olm::encode_base64_length(input_length);
 assert_equals(std::size_t(15), output_length);
 
-std::uint8_t output[output_length];
+std::uint8_t output[15];
 olm::encode_base64(input, input_length, output);
 assert_equals(expected_output, output, output_length);
 }
@@ -29,7 +29,7 @@ std::size_t input_length = sizeof(input) - 1;
 std::size_t output_length = ::_olm_encode_base64_length(input_length);
 assert_equals(std::size_t(15), output_length);
 
-std::uint8_t output[output_length];
+std::uint8_t output[15];
 output_length = ::_olm_encode_base64(input, input_length, output);
 assert_equals(std::size_t(15), output_length);
 assert_equals(expected_output, output, output_length);
@@ -45,7 +45,7 @@ std::size_t input_length = sizeof(input) - 1;
 std::size_t output_length = olm::decode_base64_length(input_length);
 assert_equals(std::size_t(11), output_length);
 
-std::uint8_t output[output_length];
+std::uint8_t output[11];
 olm::decode_base64(input, input_length, output);
 assert_equals(expected_output, output, output_length);
 }
@@ -60,7 +60,7 @@ std::size_t input_length = sizeof(input) - 1;
 std::size_t output_length = ::_olm_decode_base64_length(input_length);
 assert_equals(std::size_t(11), output_length);
 
-std::uint8_t output[output_length];
+std::uint8_t output[11];
 output_length = ::_olm_decode_base64(input, input_length, output);
 assert_equals(std::size_t(11), output_length);
 assert_equals(expected_output, output, output_length);
diff --git a/tests/test_crypto.cpp b/tests/test_crypto.cpp
index 7dad892..5da742c 100644
--- a/tests/test_crypto.cpp
+++ b/tests/test_crypto.cpp
@@ -146,7 +146,10 @@ assert_equals(input, actual, length);
 
 TestCase test_case("SHA 256 Test Case 1");
 
-std::uint8_t input[0] = {};
+// we want to take the hash of the empty string, but MSVC doesn't like
+// allocating 0 bytes, so allocate one item, but pass a length of zero to
+// sha256
+std::uint8_t input[1] = {0};
 
 std::uint8_t expected[32] = {
     0xE3, 0xB0, 0xC4, 0x42, 0x98, 0xFC, 0x1C, 0x14,
@@ -157,7 +160,7 @@ std::uint8_t expected[32] = {
 
 std::uint8_t actual[32];
 
-_olm_crypto_sha256(input, sizeof(input), actual);
+_olm_crypto_sha256(input, 0, actual);
 
 assert_equals(expected, actual, 32);
 
@@ -167,7 +170,10 @@ assert_equals(expected, actual, 32);
 
 TestCase test_case("HMAC Test Case 1");
 
-std::uint8_t input[0] = {};
+// we want to take the hash of the empty string, but MSVC doesn't like
+// allocating 0 bytes, so allocate one item, but pass a length of zero to
+// hmac_sha256
+std::uint8_t input[1] = {0};
 
 std::uint8_t expected[32] = {
     0xb6, 0x13, 0x67, 0x9a, 0x08, 0x14, 0xd9, 0xec,
@@ -178,7 +184,7 @@ std::uint8_t expected[32] = {
 
 std::uint8_t actual[32];
 
-_olm_crypto_hmac_sha256(input, sizeof(input), input, sizeof(input), actual);
+_olm_crypto_hmac_sha256(input, 0, input, 0, actual);
 
 assert_equals(expected, actual, 32);
 
diff --git a/tests/test_group_session.cpp b/tests/test_group_session.cpp
index 63241d5..19b7761 100644
--- a/tests/test_group_session.cpp
+++ b/tests/test_group_session.cpp
@@ -16,6 +16,7 @@
 #include "olm/outbound_group_session.h"
 #include "unittest.hh"
 
+#include <vector>
 
 int main() {
 
@@ -23,33 +24,32 @@ int main() {
     TestCase test_case("Pickle outbound group session");
 
     size_t size = olm_outbound_group_session_size();
-    uint8_t memory[size];
-    OlmOutboundGroupSession *session = olm_outbound_group_session(memory);
+    std::vector<uint8_t> memory(size);
+    OlmOutboundGroupSession *session = olm_outbound_group_session(memory.data());
 
     size_t pickle_length = olm_pickle_outbound_group_session_length(session);
-    uint8_t pickle1[pickle_length];
+    std::vector<uint8_t> pickle1(pickle_length);
     size_t res = olm_pickle_outbound_group_session(
-        session, "secret_key", 10, pickle1, pickle_length
+        session, "secret_key", 10, pickle1.data(), pickle_length
     );
     assert_equals(pickle_length, res);
 
-    uint8_t pickle2[pickle_length];
-    memcpy(pickle2, pickle1, pickle_length);
+    std::vector<uint8_t> pickle2(pickle1);
 
-    uint8_t buffer2[size];
-    OlmOutboundGroupSession *session2 = olm_outbound_group_session(buffer2);
+    std::vector<uint8_t> buffer2(size);
+    OlmOutboundGroupSession *session2 = olm_outbound_group_session(buffer2.data());
     res = olm_unpickle_outbound_group_session(
-        session2, "secret_key", 10, pickle2, pickle_length
+        session2, "secret_key", 10, pickle2.data(), pickle_length
     );
     assert_not_equals((size_t)-1, res);
     assert_equals(pickle_length,
                   olm_pickle_outbound_group_session_length(session2));
     res = olm_pickle_outbound_group_session(
-        session2, "secret_key", 10, pickle2, pickle_length
+        session2, "secret_key", 10, pickle2.data(), pickle_length
     );
     assert_equals(pickle_length, res);
 
-    assert_equals(pickle1, pickle2, pickle_length);
+    assert_equals(pickle1.data(), pickle2.data(), pickle_length);
 }
 
 
@@ -57,32 +57,31 @@ int main() {
     TestCase test_case("Pickle inbound group session");
 
     size_t size = olm_inbound_group_session_size();
-    uint8_t memory[size];
-    OlmInboundGroupSession *session = olm_inbound_group_session(memory);
+    std::vector<uint8_t> memory(size);
+    OlmInboundGroupSession *session = olm_inbound_group_session(memory.data());
 
     size_t pickle_length = olm_pickle_inbound_group_session_length(session);
-    uint8_t pickle1[pickle_length];
+    std::vector<uint8_t> pickle1(pickle_length);
     size_t res = olm_pickle_inbound_group_session(
-        session, "secret_key", 10, pickle1, pickle_length
+        session, "secret_key", 10, pickle1.data(), pickle_length
     );
     assert_equals(pickle_length, res);
 
-    uint8_t pickle2[pickle_length];
-    memcpy(pickle2, pickle1, pickle_length);
+    std::vector<uint8_t> pickle2(pickle1);
 
-    uint8_t buffer2[size];
-    OlmInboundGroupSession *session2 = olm_inbound_group_session(buffer2);
+    std::vector<uint8_t> buffer2(size);
+    OlmInboundGroupSession *session2 = olm_inbound_group_session(buffer2.data());
     res = olm_unpickle_inbound_group_session(
-        session2, "secret_key", 10, pickle2, pickle_length
+        session2, "secret_key", 10, pickle2.data(), pickle_length
     );
     assert_not_equals((size_t)-1, res);
     assert_equals(pickle_length,
                   olm_pickle_inbound_group_session_length(session2));
     res = olm_pickle_inbound_group_session(
-        session2, "secret_key", 10, pickle2, pickle_length
+        session2, "secret_key", 10, pickle2.data(), pickle_length
     );
 
-    assert_equals(pickle1, pickle2, pickle_length);
+    assert_equals(pickle1.data(), pickle2.data(), pickle_length);
 }
 
 {
@@ -99,8 +98,8 @@ int main() {
 
     /* build the outbound session */
     size_t size = olm_outbound_group_session_size();
-    uint8_t memory[size];
-    OlmOutboundGroupSession *session = olm_outbound_group_session(memory);
+    std::vector<uint8_t> memory(size);
+    OlmOutboundGroupSession *session = olm_outbound_group_session(memory.data());
 
     assert_equals((size_t)160,
                   olm_init_outbound_group_session_random_length(session));
@@ -111,8 +110,8 @@ int main() {
 
     assert_equals(0U, olm_outbound_group_session_message_index(session));
     size_t session_key_len = olm_outbound_group_session_key_length(session);
-    uint8_t session_key[session_key_len];
-    olm_outbound_group_session_key(session, session_key, session_key_len);
+    std::vector<uint8_t> session_key(session_key_len);
+    olm_outbound_group_session_key(session, session_key.data(), session_key_len);
 
     /* encode the message */
     uint8_t plaintext[] = "Message";
@@ -121,57 +120,56 @@ int main() {
     size_t msglen = olm_group_encrypt_message_length(
         session, plaintext_length);
 
-    uint8_t msg[msglen];
+    std::vector<uint8_t> msg(msglen);
     res = olm_group_encrypt(session, plaintext, plaintext_length,
-                            msg, msglen);
+                            msg.data(), msglen);
     assert_equals(msglen, res);
     assert_equals(1U, olm_outbound_group_session_message_index(session));
 
     /* build the inbound session */
     size = olm_inbound_group_session_size();
-    uint8_t inbound_session_memory[size];
+    std::vector<uint8_t> inbound_session_memory(size);
     OlmInboundGroupSession *inbound_session =
-        olm_inbound_group_session(inbound_session_memory);
+        olm_inbound_group_session(inbound_session_memory.data());
 
     assert_equals(0, olm_inbound_group_session_is_verified(inbound_session));
 
     res = olm_init_inbound_group_session(
-        inbound_session, session_key, session_key_len);
+        inbound_session, session_key.data(), session_key_len);
     assert_equals((size_t)0, res);
     assert_equals(1, olm_inbound_group_session_is_verified(inbound_session));
 
     /* Check the session ids */
 
     size_t out_session_id_len = olm_outbound_group_session_id_length(session);
-    uint8_t out_session_id[out_session_id_len];
+    std::vector<uint8_t> out_session_id(out_session_id_len);
     assert_equals(out_session_id_len, olm_outbound_group_session_id(
-        session, out_session_id, out_session_id_len
+        session, out_session_id.data(), out_session_id_len
     ));
 
     size_t in_session_id_len = olm_inbound_group_session_id_length(
         inbound_session
     );
-    uint8_t in_session_id[in_session_id_len];
+    std::vector<uint8_t> in_session_id(in_session_id_len);
     assert_equals(in_session_id_len, olm_inbound_group_session_id(
-        inbound_session, in_session_id, in_session_id_len
+        inbound_session, in_session_id.data(), in_session_id_len
     ));
 
     assert_equals(in_session_id_len, out_session_id_len);
-    assert_equals(out_session_id, in_session_id, in_session_id_len);
+    assert_equals(out_session_id.data(), in_session_id.data(), in_session_id_len);
 
     /* decode the message */
 
     /* olm_group_decrypt_max_plaintext_length destroys the input so we have to
        copy it. */
-    uint8_t msgcopy[msglen];
-    memcpy(msgcopy, msg, msglen);
-    size = olm_group_decrypt_max_plaintext_length(inbound_session, msgcopy, msglen);
-    uint8_t plaintext_buf[size];
+    std::vector<uint8_t> msgcopy(msg);
+    size = olm_group_decrypt_max_plaintext_length(inbound_session, msgcopy.data(), msglen);
+    std::vector<uint8_t> plaintext_buf(size);
     uint32_t message_index;
-    res = olm_group_decrypt(inbound_session, msg, msglen,
-                            plaintext_buf, size, &message_index);
+    res = olm_group_decrypt(inbound_session, msg.data(), msglen,
+                            plaintext_buf.data(), size, &message_index);
     assert_equals(plaintext_length, res);
-    assert_equals(plaintext, plaintext_buf, res);
+    assert_equals(plaintext, plaintext_buf.data(), res);
     assert_equals(message_index, uint32_t(0));
 }
 
@@ -192,9 +190,9 @@ int main() {
 
     /* init first inbound group session, and decrypt */
     std::size_t size = olm_inbound_group_session_size();
-    uint8_t session_memory1[size];
+    std::vector<uint8_t> session_memory1(size);
     OlmInboundGroupSession *session1 =
-        olm_inbound_group_session(session_memory1);
+        olm_inbound_group_session(session_memory1.data());
     assert_equals(0, olm_inbound_group_session_is_verified(session1));
 
     std::size_t res = olm_init_inbound_group_session(
@@ -205,24 +203,24 @@ int main() {
 
     /* olm_group_decrypt_max_plaintext_length destroys the input so we have to
        copy it. */
-    uint8_t msgcopy[msglen];
-    memcpy(msgcopy, message, msglen);
-    size = olm_group_decrypt_max_plaintext_length(session1, msgcopy, msglen);
-    uint8_t plaintext_buf[size];
+    std::vector<uint8_t> msgcopy(msglen);
+    memcpy(msgcopy.data(), message, msglen);
+    size = olm_group_decrypt_max_plaintext_length(session1, msgcopy.data(), msglen);
+    std::vector<uint8_t> plaintext_buf(size);
     uint32_t message_index;
-    memcpy(msgcopy, message, msglen);
+    memcpy(msgcopy.data(), message, msglen);
     res = olm_group_decrypt(
-        session1, msgcopy, msglen, plaintext_buf, size, &message_index
+        session1, msgcopy.data(), msglen, plaintext_buf.data(), size, &message_index
     );
     assert_equals((std::size_t)7, res);
-    assert_equals((const uint8_t *)"Message", plaintext_buf, res);
+    assert_equals((const uint8_t *)"Message", plaintext_buf.data(), res);
     assert_equals(uint32_t(0), message_index);
 
     /* export the keys */
     size = olm_export_inbound_group_session_length(session1);
-    uint8_t export_memory[size];
+    std::vector<uint8_t> export_memory(size);
     res = olm_export_inbound_group_session(
-        session1, export_memory, size, 0
+        session1, export_memory.data(), size, 0
     );
     assert_equals(size, res);
 
@@ -231,25 +229,25 @@ int main() {
 
     /* import the keys into another inbound group session */
     size = olm_inbound_group_session_size();
-    uint8_t session_memory2[size];
+    std::vector<uint8_t> session_memory2(size);
     OlmInboundGroupSession *session2 =
-        olm_inbound_group_session(session_memory2);
+        olm_inbound_group_session(session_memory2.data());
     res = olm_import_inbound_group_session(
-        session2, export_memory, sizeof(export_memory)
+        session2, export_memory.data(), export_memory.size()
     );
     assert_equals((size_t)0, res);
     assert_equals(0, olm_inbound_group_session_is_verified(session2));
 
     /* decrypt the message with the new session */
-    memcpy(msgcopy, message, msglen);
-    size = olm_group_decrypt_max_plaintext_length(session2, msgcopy, msglen);
-    uint8_t plaintext_buf2[size];
-    memcpy(msgcopy, message, msglen);
+    memcpy(msgcopy.data(), message, msglen);
+    size = olm_group_decrypt_max_plaintext_length(session2, msgcopy.data(), msglen);
+    std::vector<uint8_t> plaintext_buf2(size);
+    memcpy(msgcopy.data(), message, msglen);
     res = olm_group_decrypt(
-        session2, msgcopy, msglen, plaintext_buf2, size, &message_index
+        session2, msgcopy.data(), msglen, plaintext_buf2.data(), size, &message_index
     );
     assert_equals((std::size_t)7, res);
-    assert_equals((const uint8_t *)"Message", plaintext_buf2, res);
+    assert_equals((const uint8_t *)"Message", plaintext_buf2.data(), res);
     assert_equals(uint32_t(0), message_index);
     assert_equals(1, olm_inbound_group_session_is_verified(session2));
 }
@@ -274,9 +272,9 @@ int main() {
 
     /* build the inbound session */
     size_t size = olm_inbound_group_session_size();
-    uint8_t inbound_session_memory[size];
+    std::vector<uint8_t> inbound_session_memory(size);
     OlmInboundGroupSession *inbound_session =
-        olm_inbound_group_session(inbound_session_memory);
+        olm_inbound_group_session(inbound_session_memory.data());
 
     size_t res = olm_init_inbound_group_session(
         inbound_session, session_key, sizeof(session_key)-1
@@ -287,36 +285,36 @@ int main() {
 
     /* olm_group_decrypt_max_plaintext_length destroys the input so we have to
        copy it. */
-    uint8_t msgcopy[msglen];
-    memcpy(msgcopy, message, msglen);
+    std::vector<uint8_t> msgcopy(msglen);
+    memcpy(msgcopy.data(), message, msglen);
     size = olm_group_decrypt_max_plaintext_length(
-        inbound_session, msgcopy, msglen
+        inbound_session, msgcopy.data(), msglen
     );
 
-    memcpy(msgcopy, message, msglen);
-    uint8_t plaintext_buf[size];
+    memcpy(msgcopy.data(), message, msglen);
+    std::vector<uint8_t> plaintext_buf(size);
     uint32_t message_index;
     res = olm_group_decrypt(
-        inbound_session, msgcopy, msglen, plaintext_buf, size, &message_index
+        inbound_session, msgcopy.data(), msglen, plaintext_buf.data(), size, &message_index
     );
     assert_equals(message_index, uint32_t(0));
     assert_equals(plaintext_length, res);
-    assert_equals(plaintext, plaintext_buf, res);
+    assert_equals(plaintext, plaintext_buf.data(), res);
 
     /* now twiddle the signature */
     message[msglen-1] = 'E';
-    memcpy(msgcopy, message, msglen);
+    memcpy(msgcopy.data(), message, msglen);
     assert_equals(
         size,
         olm_group_decrypt_max_plaintext_length(
-            inbound_session, msgcopy, msglen
+            inbound_session, msgcopy.data(), msglen
         )
     );
 
-    memcpy(msgcopy, message, msglen);
+    memcpy(msgcopy.data(), message, msglen);
     res = olm_group_decrypt(
-        inbound_session, msgcopy, msglen,
-        plaintext_buf, size, &message_index
+        inbound_session, msgcopy.data(), msglen,
+        plaintext_buf.data(), size, &message_index
     );
     assert_equals((size_t)-1, res);
     assert_equals(
diff --git a/tests/test_message.cpp b/tests/test_message.cpp
index 25693f5..fa2d0cc 100644
--- a/tests/test_message.cpp
+++ b/tests/test_message.cpp
@@ -49,7 +49,7 @@ TestCase test_case("Message encode test");
 std::size_t length = olm::encode_message_length(1, 10, 10, 8);
 assert_equals(std::size_t(35), length);
 
-std::uint8_t output[length];
+std::uint8_t output[35];
 
 olm::MessageWriter writer;
 olm::encode_message(writer, 3, 1, 10, 10, output);
diff --git a/tests/test_olm.cpp b/tests/test_olm.cpp
index b24cd90..ab7d816 100644
--- a/tests/test_olm.cpp
+++ b/tests/test_olm.cpp
@@ -4,6 +4,7 @@
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
+#include <vector>
 
 struct MockRandom {
     MockRandom(std::uint8_t tag, std::uint8_t offset = 0)
@@ -36,35 +37,34 @@ TestCase test_case("Pickle account test");
 MockRandom mock_random('P');
 
 
-std::uint8_t account_buffer[::olm_account_size()];
-::OlmAccount *account = ::olm_account(account_buffer);
-std::uint8_t random[::olm_create_account_random_length(account)];
-mock_random(random, sizeof(random));
-::olm_create_account(account, random, sizeof(random));
-std::uint8_t ot_random[::olm_account_generate_one_time_keys_random_length(
+std::vector<std::uint8_t> account_buffer(::olm_account_size());
+::OlmAccount *account = ::olm_account(account_buffer.data());
+std::vector<std::uint8_t> random(::olm_create_account_random_length(account));
+mock_random(random.data(), random.size());
+::olm_create_account(account, random.data(), random.size());
+std::vector<std::uint8_t> ot_random(::olm_account_generate_one_time_keys_random_length(
     account, 42
-)];
-mock_random(ot_random, sizeof(ot_random));
-::olm_account_generate_one_time_keys(account, 42, ot_random, sizeof(ot_random));
+                                        ));
+mock_random(ot_random.data(), ot_random.size());
+::olm_account_generate_one_time_keys(account, 42, ot_random.data(), ot_random.size());
 
 std::size_t pickle_length = ::olm_pickle_account_length(account);
-std::uint8_t pickle1[pickle_length];
-std::size_t res = ::olm_pickle_account(account, "secret_key", 10, pickle1, pickle_length);
+std::vector<std::uint8_t> pickle1(pickle_length);
+std::size_t res = ::olm_pickle_account(account, "secret_key", 10, pickle1.data(), pickle_length);
 assert_equals(pickle_length, res);
 
-std::uint8_t pickle2[pickle_length];
-std::memcpy(pickle2, pickle1, pickle_length);
+std::vector<std::uint8_t> pickle2(pickle1);
 
-std::uint8_t account_buffer2[::olm_account_size()];
-::OlmAccount *account2 = ::olm_account(account_buffer2);
+std::vector<std::uint8_t> account_buffer2(::olm_account_size());
+::OlmAccount *account2 = ::olm_account(account_buffer2.data());
 assert_not_equals(std::size_t(-1), ::olm_unpickle_account(
-    account2, "secret_key", 10, pickle2, pickle_length
+    account2, "secret_key", 10, pickle2.data(), pickle_length
 ));
 assert_equals(pickle_length, ::olm_pickle_account_length(account2));
-res = ::olm_pickle_account(account2, "secret_key", 10, pickle2, pickle_length);
+res = ::olm_pickle_account(account2, "secret_key", 10, pickle2.data(), pickle_length);
 assert_equals(pickle_length, res);
 
-assert_equals(pickle1, pickle2, pickle_length);
+assert_equals(pickle1.data(), pickle2.data(), pickle_length);
 }
 
 
@@ -79,8 +79,8 @@ assert_equals(pickle1, pickle2, pickle_length);
         "K/A/8TOu9iK2hDFszy6xETiousHnHgh2ZGbRUh4pQx+YMm8ZdNZeRnwFGLnrWyf9"
         "O5TmXua1FcU";
 
-    std::uint8_t account_buffer[::olm_account_size()];
-    ::OlmAccount *account = ::olm_account(account_buffer);
+    std::vector<std::uint8_t> account_buffer(::olm_account_size());
+    ::OlmAccount *account = ::olm_account(account_buffer.data());
     assert_equals(
         std::size_t(-1),
         ::olm_unpickle_account(
@@ -99,47 +99,46 @@ assert_equals(pickle1, pickle2, pickle_length);
 TestCase test_case("Pickle session test");
 MockRandom mock_random('P');
 
-std::uint8_t account_buffer[::olm_account_size()];
-::OlmAccount *account = ::olm_account(account_buffer);
-std::uint8_t random[::olm_create_account_random_length(account)];
-mock_random(random, sizeof(random));
-::olm_create_account(account, random, sizeof(random));
+std::vector<std::uint8_t> account_buffer(::olm_account_size());
+::OlmAccount *account = ::olm_account(account_buffer.data());
+std::vector<std::uint8_t> random(::olm_create_account_random_length(account));
+mock_random(random.data(), random.size());
+::olm_create_account(account, random.data(), random.size());
 
-std::uint8_t session_buffer[::olm_session_size()];
-::OlmSession *session = ::olm_session(session_buffer);
+std::vector<std::uint8_t> session_buffer(::olm_session_size());
+::OlmSession *session = ::olm_session(session_buffer.data());
 std::uint8_t identity_key[32];
 std::uint8_t one_time_key[32];
 mock_random(identity_key, sizeof(identity_key));
 mock_random(one_time_key, sizeof(one_time_key));
-std::uint8_t random2[::olm_create_outbound_session_random_length(session)];
-mock_random(random2, sizeof(random2));
+std::vector<std::uint8_t> random2(::olm_create_outbound_session_random_length(session));
+mock_random(random2.data(), random2.size());
 
 ::olm_create_outbound_session(
     session, account,
     identity_key, sizeof(identity_key),
     one_time_key, sizeof(one_time_key),
-    random2, sizeof(random2)
+    random2.data(), random2.size()
 );
 
 
 std::size_t pickle_length = ::olm_pickle_session_length(session);
-std::uint8_t pickle1[pickle_length];
-std::size_t res = ::olm_pickle_session(session, "secret_key", 10, pickle1, pickle_length);
+std::vector<std::uint8_t> pickle1(pickle_length);
+std::size_t res = ::olm_pickle_session(session, "secret_key", 10, pickle1.data(), pickle_length);
 assert_equals(pickle_length, res);
 
-std::uint8_t pickle2[pickle_length];
-std::memcpy(pickle2, pickle1, pickle_length);
+std::vector<std::uint8_t> pickle2(pickle1);
 
-std::uint8_t session_buffer2[::olm_session_size()];
-::OlmSession *session2 = ::olm_session(session_buffer2);
+std::vector<std::uint8_t> session_buffer2(::olm_session_size());
+::OlmSession *session2 = ::olm_session(session_buffer2.data());
 assert_not_equals(std::size_t(-1), ::olm_unpickle_session(
-    session2, "secret_key", 10, pickle2, pickle_length
+    session2, "secret_key", 10, pickle2.data(), pickle_length
 ));
 assert_equals(pickle_length, ::olm_pickle_session_length(session2));
-res = ::olm_pickle_session(session2, "secret_key", 10, pickle2, pickle_length);
+res = ::olm_pickle_session(session2, "secret_key", 10, pickle2.data(), pickle_length);
 assert_equals(pickle_length, res);
 
-assert_equals(pickle1, pickle2, pickle_length);
+assert_equals(pickle1.data(), pickle2.data(), pickle_length);
 }
 
 { /** Loopback test */
@@ -148,145 +147,143 @@ TestCase test_case("Loopback test");
 MockRandom mock_random_a('A', 0x00);
 MockRandom mock_random_b('B', 0x80);
 
-std::uint8_t a_account_buffer[::olm_account_size()];
-::OlmAccount *a_account = ::olm_account(a_account_buffer);
-std::uint8_t a_random[::olm_create_account_random_length(a_account)];
-mock_random_a(a_random, sizeof(a_random));
-::olm_create_account(a_account, a_random, sizeof(a_random));
+std::vector<std::uint8_t> a_account_buffer(::olm_account_size());
+::OlmAccount *a_account = ::olm_account(a_account_buffer.data());
+std::vector<std::uint8_t> a_random(::olm_create_account_random_length(a_account));
+mock_random_a(a_random.data(), a_random.size());
+::olm_create_account(a_account, a_random.data(), a_random.size());
 
-std::uint8_t b_account_buffer[::olm_account_size()];
-::OlmAccount *b_account = ::olm_account(b_account_buffer);
-std::uint8_t b_random[::olm_create_account_random_length(b_account)];
-mock_random_b(b_random, sizeof(b_random));
-::olm_create_account(b_account, b_random, sizeof(b_random));
-std::uint8_t o_random[::olm_account_generate_one_time_keys_random_length(
+std::vector<std::uint8_t> b_account_buffer(::olm_account_size());
+::OlmAccount *b_account = ::olm_account(b_account_buffer.data());
+std::vector<std::uint8_t> b_random(::olm_create_account_random_length(b_account));
+mock_random_b(b_random.data(), b_random.size());
+::olm_create_account(b_account, b_random.data(), b_random.size());
+std::vector<std::uint8_t> o_random(::olm_account_generate_one_time_keys_random_length(
         b_account, 42
-)];
-mock_random_b(o_random, sizeof(o_random));
-::olm_account_generate_one_time_keys(b_account, 42, o_random, sizeof(o_random));
+));
+mock_random_b(o_random.data(), o_random.size());
+::olm_account_generate_one_time_keys(b_account, 42, o_random.data(), o_random.size());
 
-std::uint8_t a_id_keys[::olm_account_identity_keys_length(a_account)];
-::olm_account_identity_keys(a_account, a_id_keys, sizeof(a_id_keys));
+std::vector<std::uint8_t> a_id_keys(::olm_account_identity_keys_length(a_account));
+::olm_account_identity_keys(a_account, a_id_keys.data(), a_id_keys.size());
 
-std::uint8_t b_id_keys[::olm_account_identity_keys_length(b_account)];
-std::uint8_t b_ot_keys[::olm_account_one_time_keys_length(b_account)];
-::olm_account_identity_keys(b_account, b_id_keys, sizeof(b_id_keys));
-::olm_account_one_time_keys(b_account, b_ot_keys, sizeof(b_ot_keys));
+std::vector<std::uint8_t> b_id_keys(::olm_account_identity_keys_length(b_account));
+std::vector<std::uint8_t> b_ot_keys(::olm_account_one_time_keys_length(b_account));
+::olm_account_identity_keys(b_account, b_id_keys.data(), b_id_keys.size());
+::olm_account_one_time_keys(b_account, b_ot_keys.data(), b_ot_keys.size());
 
-std::uint8_t a_session_buffer[::olm_session_size()];
-::OlmSession *a_session = ::olm_session(a_session_buffer);
-std::uint8_t a_rand[::olm_create_outbound_session_random_length(a_session)];
-mock_random_a(a_rand, sizeof(a_rand));
+std::vector<std::uint8_t> a_session_buffer(::olm_session_size());
+::OlmSession *a_session = ::olm_session(a_session_buffer.data());
+std::vector<std::uint8_t> a_rand(::olm_create_outbound_session_random_length(a_session));
+mock_random_a(a_rand.data(), a_rand.size());
 assert_not_equals(std::size_t(-1), ::olm_create_outbound_session(
     a_session, a_account,
-    b_id_keys + 15, 43, // B's curve25519 identity key
-    b_ot_keys + 25, 43, // B's curve25519 one time key
-    a_rand, sizeof(a_rand)
+    b_id_keys.data() + 15, 43, // B's curve25519 identity key
+    b_ot_keys.data() + 25, 43, // B's curve25519 one time key
+    a_rand.data(), a_rand.size()
 ));
 
 std::uint8_t plaintext[] = "Hello, World";
-std::uint8_t message_1[::olm_encrypt_message_length(a_session, 12)];
-std::uint8_t a_message_random[::olm_encrypt_random_length(a_session)];
-mock_random_a(a_message_random, sizeof(a_message_random));
+std::vector<std::uint8_t> message_1(::olm_encrypt_message_length(a_session, 12));
+std::vector<std::uint8_t> a_message_random(::olm_encrypt_random_length(a_session));
+mock_random_a(a_message_random.data(), a_message_random.size());
 assert_equals(std::size_t(0), ::olm_encrypt_message_type(a_session));
 assert_not_equals(std::size_t(-1), ::olm_encrypt(
     a_session,
     plaintext, 12,
-    a_message_random, sizeof(a_message_random),
-    message_1, sizeof(message_1)
+    a_message_random.data(), a_message_random.size(),
+    message_1.data(), message_1.size()
 ));
 
 
-std::uint8_t tmp_message_1[sizeof(message_1)];
-std::memcpy(tmp_message_1, message_1, sizeof(message_1));
-std::uint8_t b_session_buffer[::olm_account_size()];
-::OlmSession *b_session = ::olm_session(b_session_buffer);
+std::vector<std::uint8_t> tmp_message_1(message_1);
+std::vector<std::uint8_t> b_session_buffer(::olm_account_size());
+::OlmSession *b_session = ::olm_session(b_session_buffer.data());
 ::olm_create_inbound_session(
-    b_session, b_account, tmp_message_1, sizeof(message_1)
+    b_session, b_account, tmp_message_1.data(), message_1.size()
 );
 
 // Check that the inbound session matches the message it was created from.
-std::memcpy(tmp_message_1, message_1, sizeof(message_1));
+std::memcpy(tmp_message_1.data(), message_1.data(), message_1.size());
 assert_equals(std::size_t(1), ::olm_matches_inbound_session(
     b_session,
-    tmp_message_1, sizeof(message_1)
+    tmp_message_1.data(), message_1.size()
 ));
 
 // Check that the inbound session matches the key this message is supposed
 // to be from.
-std::memcpy(tmp_message_1, message_1, sizeof(message_1));
+std::memcpy(tmp_message_1.data(), message_1.data(), message_1.size());
 assert_equals(std::size_t(1), ::olm_matches_inbound_session_from(
     b_session,
-    a_id_keys + 15, 43, // A's curve125519 identity key.
-    tmp_message_1, sizeof(message_1)
+    a_id_keys.data() + 15, 43, // A's curve125519 identity key.
+    tmp_message_1.data(), message_1.size()
 ));
 
 // Check that the inbound session isn't from a different user.
-std::memcpy(tmp_message_1, message_1, sizeof(message_1));
+std::memcpy(tmp_message_1.data(), message_1.data(), message_1.size());
 assert_equals(std::size_t(0), ::olm_matches_inbound_session_from(
     b_session,
-    b_id_keys + 15, 43, // B's curve25519 identity key.
-    tmp_message_1, sizeof(message_1)
+    b_id_keys.data() + 15, 43, // B's curve25519 identity key.
+    tmp_message_1.data(), message_1.size()
 ));
 
 // Check that we can decrypt the message.
-std::memcpy(tmp_message_1, message_1, sizeof(message_1));
-std::uint8_t plaintext_1[::olm_decrypt_max_plaintext_length(
-    b_session, 0, tmp_message_1, sizeof(message_1)
-)];
-std::memcpy(tmp_message_1, message_1, sizeof(message_1));
+std::memcpy(tmp_message_1.data(), message_1.data(), message_1.size());
+std::vector<std::uint8_t> plaintext_1(::olm_decrypt_max_plaintext_length(
+    b_session, 0, tmp_message_1.data(), message_1.size()
+));
+std::memcpy(tmp_message_1.data(), message_1.data(), message_1.size());
 assert_equals(std::size_t(12), ::olm_decrypt(
     b_session, 0,
-    tmp_message_1, sizeof(message_1),
-    plaintext_1, sizeof(plaintext_1)
+    tmp_message_1.data(), message_1.size(),
+    plaintext_1.data(), plaintext_1.size()
 ));
 
-assert_equals(plaintext, plaintext_1, 12);
+assert_equals(plaintext, plaintext_1.data(), 12);
 
-std::uint8_t message_2[::olm_encrypt_message_length(b_session, 12)];
-std::uint8_t b_message_random[::olm_encrypt_random_length(b_session)];
-mock_random_b(b_message_random, sizeof(b_message_random));
+std::vector<std::uint8_t> message_2(::olm_encrypt_message_length(b_session, 12));
+std::vector<std::uint8_t> b_message_random(::olm_encrypt_random_length(b_session));
+mock_random_b(b_message_random.data(), b_message_random.size());
 assert_equals(std::size_t(1), ::olm_encrypt_message_type(b_session));
 assert_not_equals(std::size_t(-1), ::olm_encrypt(
     b_session,
     plaintext, 12,
-    b_message_random, sizeof(b_message_random),
-    message_2, sizeof(message_2)
+    b_message_random.data(), b_message_random.size(),
+    message_2.data(), message_2.size()
 ));
 
-std::uint8_t tmp_message_2[sizeof(message_2)];
-std::memcpy(tmp_message_2, message_2, sizeof(message_2));
-std::uint8_t plaintext_2[::olm_decrypt_max_plaintext_length(
-    a_session, 1, tmp_message_2, sizeof(message_2)
-)];
-std::memcpy(tmp_message_2, message_2, sizeof(message_2));
+std::vector<std::uint8_t> tmp_message_2(message_2);
+std::vector<std::uint8_t> plaintext_2(::olm_decrypt_max_plaintext_length(
+    a_session, 1, tmp_message_2.data(), message_2.size()
+));
+std::memcpy(tmp_message_2.data(), message_2.data(), message_2.size());
 assert_equals(std::size_t(12), ::olm_decrypt(
     a_session, 1,
-    tmp_message_2, sizeof(message_2),
-    plaintext_2, sizeof(plaintext_2)
+    tmp_message_2.data(), message_2.size(),
+    plaintext_2.data(), plaintext_2.size()
 ));
 
-assert_equals(plaintext, plaintext_2, 12);
+assert_equals(plaintext, plaintext_2.data(), 12);
 
-std::memcpy(tmp_message_2, message_2, sizeof(message_2));
+std::memcpy(tmp_message_2.data(), message_2.data(), message_2.size());
 assert_equals(std::size_t(-1), ::olm_decrypt(
     a_session, 1,
-    tmp_message_2, sizeof(message_2),
-    plaintext_2, sizeof(plaintext_2)
+    tmp_message_2.data(), message_2.size(),
+    plaintext_2.data(), plaintext_2.size()
 ));
 
-std::uint8_t a_session_id[::olm_session_id_length(a_session)];
+std::vector<std::uint8_t> a_session_id(::olm_session_id_length(a_session));
 assert_not_equals(std::size_t(-1), ::olm_session_id(
-    a_session, a_session_id, sizeof(a_session_id)
+    a_session, a_session_id.data(), a_session_id.size()
 ));
 
-std::uint8_t b_session_id[::olm_session_id_length(b_session)];
+std::vector<std::uint8_t> b_session_id(::olm_session_id_length(b_session));
 assert_not_equals(std::size_t(-1), ::olm_session_id(
-    b_session, b_session_id, sizeof(b_session_id)
+    b_session, b_session_id.data(), b_session_id.size()
 ));
 
-assert_equals(sizeof(a_session_id), sizeof(b_session_id));
-assert_equals(a_session_id, b_session_id, sizeof(b_session_id));
+assert_equals(a_session_id.size(), b_session_id.size());
+assert_equals(a_session_id.data(), b_session_id.data(), b_session_id.size());
 
 }
 
@@ -296,107 +293,104 @@ TestCase test_case("More messages test");
 MockRandom mock_random_a('A', 0x00);
 MockRandom mock_random_b('B', 0x80);
 
-std::uint8_t a_account_buffer[::olm_account_size()];
-::OlmAccount *a_account = ::olm_account(a_account_buffer);
-std::uint8_t a_random[::olm_create_account_random_length(a_account)];
-mock_random_a(a_random, sizeof(a_random));
-::olm_create_account(a_account, a_random, sizeof(a_random));
+std::vector<std::uint8_t> a_account_buffer(::olm_account_size());
+::OlmAccount *a_account = ::olm_account(a_account_buffer.data());
+std::vector<std::uint8_t> a_random(::olm_create_account_random_length(a_account));
+mock_random_a(a_random.data(), a_random.size());
+::olm_create_account(a_account, a_random.data(), a_random.size());
 
-std::uint8_t b_account_buffer[::olm_account_size()];
-::OlmAccount *b_account = ::olm_account(b_account_buffer);
-std::uint8_t b_random[::olm_create_account_random_length(b_account)];
-mock_random_b(b_random, sizeof(b_random));
-::olm_create_account(b_account, b_random, sizeof(b_random));
-std::uint8_t o_random[::olm_account_generate_one_time_keys_random_length(
+std::vector<std::uint8_t> b_account_buffer(::olm_account_size());
+::OlmAccount *b_account = ::olm_account(b_account_buffer.data());
+std::vector<std::uint8_t> b_random(::olm_create_account_random_length(b_account));
+mock_random_b(b_random.data(), b_random.size());
+::olm_create_account(b_account, b_random.data(), b_random.size());
+std::vector<std::uint8_t> o_random(::olm_account_generate_one_time_keys_random_length(
         b_account, 42
-)];
-mock_random_b(o_random, sizeof(o_random));
-::olm_account_generate_one_time_keys(b_account, 42, o_random, sizeof(o_random));
+));
+mock_random_b(o_random.data(), o_random.size());
+::olm_account_generate_one_time_keys(b_account, 42, o_random.data(), o_random.size());
 
-std::uint8_t b_id_keys[::olm_account_identity_keys_length(b_account)];
-std::uint8_t b_ot_keys[::olm_account_one_time_keys_length(b_account)];
-::olm_account_identity_keys(b_account, b_id_keys, sizeof(b_id_keys));
-::olm_account_one_time_keys(b_account, b_ot_keys, sizeof(b_ot_keys));
+std::vector<std::uint8_t> b_id_keys(::olm_account_identity_keys_length(b_account));
+std::vector<std::uint8_t> b_ot_keys(::olm_account_one_time_keys_length(b_account));
+::olm_account_identity_keys(b_account, b_id_keys.data(), b_id_keys.size());
+::olm_account_one_time_keys(b_account, b_ot_keys.data(), b_ot_keys.size());
 
-std::uint8_t a_session_buffer[::olm_session_size()];
-::OlmSession *a_session = ::olm_session(a_session_buffer);
-std::uint8_t a_rand[::olm_create_outbound_session_random_length(a_session)];
-mock_random_a(a_rand, sizeof(a_rand));
+std::vector<std::uint8_t> a_session_buffer(::olm_session_size());
+::OlmSession *a_session = ::olm_session(a_session_buffer.data());
+std::vector<std::uint8_t> a_rand(::olm_create_outbound_session_random_length(a_session));
+mock_random_a(a_rand.data(), a_rand.size());
 assert_not_equals(std::size_t(-1), ::olm_create_outbound_session(
     a_session, a_account,
-    b_id_keys + 15, 43,
-    b_ot_keys + 25, 43,
-    a_rand, sizeof(a_rand)
+    b_id_keys.data() + 15, 43,
+    b_ot_keys.data() + 25, 43,
+    a_rand.data(), a_rand.size()
 ));
 
 std::uint8_t plaintext[] = "Hello, World";
-std::uint8_t message_1[::olm_encrypt_message_length(a_session, 12)];
-std::uint8_t a_message_random[::olm_encrypt_random_length(a_session)];
-mock_random_a(a_message_random, sizeof(a_message_random));
+std::vector<std::uint8_t> message_1(::olm_encrypt_message_length(a_session, 12));
+std::vector<std::uint8_t> a_message_random(::olm_encrypt_random_length(a_session));
+mock_random_a(a_message_random.data(), a_message_random.size());
 assert_equals(std::size_t(0), ::olm_encrypt_message_type(a_session));
 assert_not_equals(std::size_t(-1), ::olm_encrypt(
     a_session,
     plaintext, 12,
-    a_message_random, sizeof(a_message_random),
-    message_1, sizeof(message_1)
+    a_message_random.data(), a_message_random.size(),
+    message_1.data(), message_1.size()
 ));
 
-std::uint8_t tmp_message_1[sizeof(message_1)];
-std::memcpy(tmp_message_1, message_1, sizeof(message_1));
-std::uint8_t b_session_buffer[::olm_account_size()];
-::OlmSession *b_session = ::olm_session(b_session_buffer);
+std::vector<std::uint8_t> tmp_message_1(message_1);
+std::vector<std::uint8_t> b_session_buffer(::olm_account_size());
+::OlmSession *b_session = ::olm_session(b_session_buffer.data());
 ::olm_create_inbound_session(
-    b_session, b_account, tmp_message_1, sizeof(message_1)
+    b_session, b_account, tmp_message_1.data(), message_1.size()
 );
 
-std::memcpy(tmp_message_1, message_1, sizeof(message_1));
-std::uint8_t plaintext_1[::olm_decrypt_max_plaintext_length(
-    b_session, 0, tmp_message_1, sizeof(message_1)
-)];
-std::memcpy(tmp_message_1, message_1, sizeof(message_1));
+std::memcpy(tmp_message_1.data(), message_1.data(), message_1.size());
+std::vector<std::uint8_t> plaintext_1(::olm_decrypt_max_plaintext_length(
+    b_session, 0, tmp_message_1.data(), message_1.size()
+));
+std::memcpy(tmp_message_1.data(), message_1.data(), message_1.size());
 assert_equals(std::size_t(12), ::olm_decrypt(
     b_session, 0,
-    tmp_message_1, sizeof(message_1),
-    plaintext_1, sizeof(plaintext_1)
+    tmp_message_1.data(), message_1.size(),
+    plaintext_1.data(), plaintext_1.size()
 ));
 
 for (unsigned i = 0; i < 8; ++i) {
     {
-    std::uint8_t msg_a[::olm_encrypt_message_length(a_session, 12)];
-    std::uint8_t rnd_a[::olm_encrypt_random_length(a_session)];
-    mock_random_a(rnd_a, sizeof(rnd_a));
+    std::vector<std::uint8_t> msg_a(::olm_encrypt_message_length(a_session, 12));
+    std::vector<std::uint8_t> rnd_a(::olm_encrypt_random_length(a_session));
+    mock_random_a(rnd_a.data(), rnd_a.size());
     std::size_t type_a = ::olm_encrypt_message_type(a_session);
     assert_not_equals(std::size_t(-1), ::olm_encrypt(
-        a_session, plaintext, 12, rnd_a, sizeof(rnd_a), msg_a, sizeof(msg_a)
+        a_session, plaintext, 12, rnd_a.data(), rnd_a.size(), msg_a.data(), msg_a.size()
     ));
 
-    std::uint8_t tmp_a[sizeof(msg_a)];
-    std::memcpy(tmp_a, msg_a, sizeof(msg_a));
-    std::uint8_t out_a[::olm_decrypt_max_plaintext_length(
-        b_session, type_a, tmp_a, sizeof(tmp_a)
-    )];
-    std::memcpy(tmp_a, msg_a, sizeof(msg_a));
+    std::vector<std::uint8_t> tmp_a(msg_a);
+    std::vector<std::uint8_t> out_a(::olm_decrypt_max_plaintext_length(
+        b_session, type_a, tmp_a.data(), tmp_a.size()
+    ));
+    std::memcpy(tmp_a.data(), msg_a.data(), sizeof(msg_a));
     assert_equals(std::size_t(12), ::olm_decrypt(
-        b_session, type_a, msg_a, sizeof(msg_a), out_a, sizeof(out_a)
+        b_session, type_a, msg_a.data(), msg_a.size(), out_a.data(), out_a.size()
     ));
     }
     {
-    std::uint8_t msg_b[::olm_encrypt_message_length(b_session, 12)];
-    std::uint8_t rnd_b[::olm_encrypt_random_length(b_session)];
-    mock_random_b(rnd_b, sizeof(rnd_b));
+    std::vector<std::uint8_t> msg_b(::olm_encrypt_message_length(b_session, 12));
+    std::vector<std::uint8_t> rnd_b(::olm_encrypt_random_length(b_session));
+    mock_random_b(rnd_b.data(), rnd_b.size());
     std::size_t type_b = ::olm_encrypt_message_type(b_session);
     assert_not_equals(std::size_t(-1), ::olm_encrypt(
-        b_session, plaintext, 12, rnd_b, sizeof(rnd_b), msg_b, sizeof(msg_b)
+        b_session, plaintext, 12, rnd_b.data(), rnd_b.size(), msg_b.data(), msg_b.size()
     ));
 
-    std::uint8_t tmp_b[sizeof(msg_b)];
-    std::memcpy(tmp_b, msg_b, sizeof(msg_b));
-    std::uint8_t out_b[::olm_decrypt_max_plaintext_length(
-        a_session, type_b, tmp_b, sizeof(tmp_b)
-    )];
-    std::memcpy(tmp_b, msg_b, sizeof(msg_b));
+    std::vector<std::uint8_t> tmp_b(msg_b);
+    std::vector<std::uint8_t> out_b(::olm_decrypt_max_plaintext_length(
+        a_session, type_b, tmp_b.data(), tmp_b.size()
+    ));
+    std::memcpy(tmp_b.data(), msg_b.data(), msg_b.size());
     assert_equals(std::size_t(12), ::olm_decrypt(
-        a_session, type_b, msg_b, sizeof(msg_b), out_b, sizeof(out_b)
+        a_session, type_b, msg_b.data(), msg_b.size(), out_b.data(), out_b.size()
     ));
     }
 }
diff --git a/tests/test_olm_decrypt.cpp b/tests/test_olm_decrypt.cpp
index 4a1fb97..0c8feb8 100644
--- a/tests/test_olm_decrypt.cpp
+++ b/tests/test_olm_decrypt.cpp
@@ -1,6 +1,8 @@
 #include "olm/olm.h"
 #include "unittest.hh"
 
+#include <vector>
+
 struct test_case {
     const char *msghex;
     const char *expected_error;
@@ -37,14 +39,14 @@ void decode_hex(
 }
 
 void decrypt_case(int message_type, const test_case * test_case) {
-    std::uint8_t session_memory[olm_session_size()];
-    ::OlmSession * session = ::olm_session(session_memory);
+    std::vector<std::uint8_t> session_memory(olm_session_size());
+    ::OlmSession * session = ::olm_session(session_memory.data());
 
-    std::uint8_t pickled[strlen(session_data)];
-    ::memcpy(pickled, session_data, sizeof(pickled));
+    std::vector<std::uint8_t> pickled(strlen(session_data));
+    ::memcpy(pickled.data(), session_data, pickled.size());
     assert_not_equals(
         ::olm_error(),
-        ::olm_unpickle_session(session, "", 0, pickled, sizeof(pickled))
+        ::olm_unpickle_session(session, "", 0, pickled.data(), pickled.size())
     );
 
     std::size_t message_length = strlen(test_case->msghex) / 2;
@@ -67,12 +69,12 @@ void decrypt_case(int message_type, const test_case * test_case) {
 
     assert_not_equals(::olm_error(), max_length);
 
-    uint8_t plaintext[max_length];
+    std::vector<uint8_t> plaintext(max_length);
     decode_hex(test_case->msghex, message, message_length);
     olm_decrypt(
         session, message_type,
         message, message_length,
-        plaintext, max_length
+        plaintext.data(), max_length
     );
     free(message);
 }
diff --git a/tests/test_olm_sha256.cpp b/tests/test_olm_sha256.cpp
index c6d0242..d76e592 100644
--- a/tests/test_olm_sha256.cpp
+++ b/tests/test_olm_sha256.cpp
@@ -1,13 +1,15 @@
 #include "olm/olm.h"
 #include "unittest.hh"
 
+#include <vector>
+
 int main() {
 {
 TestCase("Olm sha256 test");
 
 
-std::uint8_t utility_buffer[::olm_utility_size()];
-::OlmUtility * utility = ::olm_utility(utility_buffer);
+std::vector<std::uint8_t> utility_buffer(::olm_utility_size());
+::OlmUtility * utility = ::olm_utility(utility_buffer.data());
 
 assert_equals(std::size_t(43), ::olm_sha256_length(utility));
 std::uint8_t output[43];
diff --git a/tests/test_pk.cpp b/tests/test_pk.cpp
index abdbda0..7679096 100644
--- a/tests/test_pk.cpp
+++ b/tests/test_pk.cpp
@@ -5,6 +5,7 @@
 #include "unittest.hh"
 
 #include <iostream>
+#include <vector>
 
 int main() {
 
@@ -13,8 +14,8 @@ int main() {
 
 TestCase test_case("Public Key Encryption/Decryption Test Case 1");
 
-std::uint8_t decryption_buffer[olm_pk_decryption_size()];
-OlmPkDecryption *decryption = olm_pk_decryption(decryption_buffer);
+std::vector<std::uint8_t> decryption_buffer(olm_pk_decryption_size());
+OlmPkDecryption *decryption = olm_pk_decryption(decryption_buffer.data());
 
 std::uint8_t alice_private[32] = {
     0x77, 0x07, 0x6D, 0x0A, 0x73, 0x18, 0xA5, 0x7D,
@@ -34,25 +35,25 @@ std::uint8_t bob_private[32] = {
 
 const std::uint8_t *bob_public = (std::uint8_t *) "3p7bfXt9wbTTW2HC7OQ1Nz+DQ8hbeGdNrfx+FG+IK08";
 
-std::uint8_t pubkey[::olm_pk_key_length()];
+std::vector<std::uint8_t> pubkey(::olm_pk_key_length());
 
 olm_pk_key_from_private(
     decryption,
-    pubkey, sizeof(pubkey),
+    pubkey.data(), pubkey.size(),
     alice_private, sizeof(alice_private)
 );
 
-assert_equals(alice_public, pubkey, olm_pk_key_length());
+assert_equals(alice_public, pubkey.data(), olm_pk_key_length());
 
 uint8_t *alice_private_back_out = (uint8_t *)malloc(olm_pk_private_key_length());
 olm_pk_get_private_key(decryption, alice_private_back_out, olm_pk_private_key_length());
 assert_equals(alice_private, alice_private_back_out, olm_pk_private_key_length());
 free(alice_private_back_out);
 
-std::uint8_t encryption_buffer[olm_pk_encryption_size()];
-OlmPkEncryption *encryption = olm_pk_encryption(encryption_buffer);
+std::vector<std::uint8_t> encryption_buffer(olm_pk_encryption_size());
+OlmPkEncryption *encryption = olm_pk_encryption(encryption_buffer.data());
 
-olm_pk_encryption_set_recipient_key(encryption, pubkey, sizeof(pubkey));
+olm_pk_encryption_set_recipient_key(encryption, pubkey.data(), pubkey.size());
 
 const size_t plaintext_length = 14;
 const std::uint8_t *plaintext = (std::uint8_t *) "This is a test";
@@ -60,27 +61,27 @@ const std::uint8_t *plaintext = (std::uint8_t *) "This is a test";
 size_t ciphertext_length = olm_pk_ciphertext_length(encryption, plaintext_length);
 std::uint8_t *ciphertext_buffer = (std::uint8_t *) malloc(ciphertext_length);
 
-std::uint8_t output_buffer[olm_pk_mac_length(encryption)];
-std::uint8_t ephemeral_key[olm_pk_key_length()];
+std::vector<std::uint8_t> output_buffer(olm_pk_mac_length(encryption));
+std::vector<std::uint8_t> ephemeral_key(olm_pk_key_length());
 
 olm_pk_encrypt(
     encryption,
     plaintext, plaintext_length,
     ciphertext_buffer, ciphertext_length,
-    output_buffer, sizeof(output_buffer),
-    ephemeral_key, sizeof(ephemeral_key),
+    output_buffer.data(), output_buffer.size(),
+    ephemeral_key.data(), ephemeral_key.size(),
     bob_private, sizeof(bob_private)
 );
 
-assert_equals(bob_public, ephemeral_key, olm_pk_key_length());
+assert_equals(bob_public, ephemeral_key.data(), olm_pk_key_length());
 
 size_t max_plaintext_length = olm_pk_max_plaintext_length(decryption, ciphertext_length);
 std::uint8_t *plaintext_buffer = (std::uint8_t *) malloc(max_plaintext_length);
 
 olm_pk_decrypt(
     decryption,
-    ephemeral_key, sizeof(ephemeral_key),
-    output_buffer, sizeof(output_buffer),
+    ephemeral_key.data(), ephemeral_key.size(),
+    output_buffer.data(), output_buffer.size(),
     ciphertext_buffer, ciphertext_length,
     plaintext_buffer, max_plaintext_length
 );
@@ -96,8 +97,8 @@ free(plaintext_buffer);
 
 TestCase test_case("Public Key Decryption pickling");
 
-std::uint8_t decryption_buffer[olm_pk_decryption_size()];
-OlmPkDecryption *decryption = olm_pk_decryption(decryption_buffer);
+std::vector<std::uint8_t> decryption_buffer(olm_pk_decryption_size());
+OlmPkDecryption *decryption = olm_pk_decryption(decryption_buffer.data());
 
 std::uint8_t alice_private[32] = {
     0x77, 0x07, 0x6D, 0x0A, 0x73, 0x18, 0xA5, 0x7D,
@@ -108,37 +109,37 @@ std::uint8_t alice_private[32] = {
 
 const std::uint8_t *alice_public = (std::uint8_t *) "hSDwCYkwp1R0i33ctD73Wg2/Og0mOBr066SpjqqbTmoK";
 
-std::uint8_t pubkey[olm_pk_key_length()];
+std::vector<std::uint8_t> pubkey(olm_pk_key_length());
 
 olm_pk_key_from_private(
     decryption,
-    pubkey, sizeof(pubkey),
+    pubkey.data(), pubkey.size(),
     alice_private, sizeof(alice_private)
 );
 
 const uint8_t *PICKLE_KEY=(uint8_t *)"secret_key";
-std::uint8_t pickle_buffer[olm_pickle_pk_decryption_length(decryption)];
+std::vector<std::uint8_t> pickle_buffer(olm_pickle_pk_decryption_length(decryption));
 const uint8_t *expected_pickle = (uint8_t *) "qx37WTQrjZLz5tId/uBX9B3/okqAbV1ofl9UnHKno1eipByCpXleAAlAZoJgYnCDOQZDQWzo3luTSfkF9pU1mOILCbbouubs6TVeDyPfgGD9i86J8irHjA";
 
 olm_pickle_pk_decryption(
     decryption,
     PICKLE_KEY, strlen((char *)PICKLE_KEY),
-    pickle_buffer, sizeof(pickle_buffer)
+    pickle_buffer.data(), pickle_buffer.size()
 );
-assert_equals(expected_pickle, pickle_buffer, olm_pickle_pk_decryption_length(decryption));
+assert_equals(expected_pickle, pickle_buffer.data(), olm_pickle_pk_decryption_length(decryption));
 
 olm_clear_pk_decryption(decryption);
 
-memset(pubkey, 0, olm_pk_key_length());
+memset(pubkey.data(), 0, olm_pk_key_length());
 
 olm_unpickle_pk_decryption(
     decryption,
     PICKLE_KEY, strlen((char *)PICKLE_KEY),
-    pickle_buffer, sizeof(pickle_buffer),
-    pubkey, sizeof(pubkey)
+    pickle_buffer.data(), pickle_buffer.size(),
+    pubkey.data(), pubkey.size()
 );
 
-assert_equals(alice_public, pubkey, olm_pk_key_length());
+assert_equals(alice_public, pubkey.data(), olm_pk_key_length());
 
 char *ciphertext = strdup("ntk49j/KozVFtSqJXhCejg");
 const char *mac = "zpzU6BkZcNI";
@@ -168,8 +169,8 @@ free(plaintext_buffer);
 
 TestCase test_case("Public Key Signing");
 
-std::uint8_t signing_buffer[olm_pk_signing_size()];
-OlmPkSigning *signing = olm_pk_signing(signing_buffer);
+std::vector<std::uint8_t> signing_buffer(olm_pk_signing_size());
+OlmPkSigning *signing = olm_pk_signing(signing_buffer.data());
 
 std::uint8_t seed[32] = {
     0x77, 0x07, 0x6D, 0x0A, 0x73, 0x18, 0xA5, 0x7D,
@@ -180,11 +181,11 @@ std::uint8_t seed[32] = {
 
 //const std::uint8_t *pub_key = (std::uint8_t *) "hSDwCYkwp1R0i33ctD73Wg2/Og0mOBr066SpjqqbTmoK";
 
-char pubkey[olm_pk_signing_public_key_length() + 1];
+std::vector<char> pubkey(olm_pk_signing_public_key_length() + 1);
 
 olm_pk_signing_key_from_seed(
     signing,
-    pubkey, sizeof(pubkey),
+    pubkey.data(), pubkey.size() - 1,
     seed, sizeof(seed)
 );
 
@@ -205,7 +206,7 @@ size_t result;
 
 result = ::olm_ed25519_verify(
     utility,
-    pubkey, olm_pk_signing_public_key_length(),
+    pubkey.data(), olm_pk_signing_public_key_length(),
     message, strlen(message),
     sig_buffer, olm_pk_signature_length()
 );
@@ -216,7 +217,7 @@ sig_buffer[5] = 'm';
 
 result = ::olm_ed25519_verify(
     utility,
-    pubkey, olm_pk_signing_public_key_length(),
+    pubkey.data(), olm_pk_signing_public_key_length(),
     message, strlen(message),
     sig_buffer, olm_pk_signature_length()
 );
diff --git a/tests/test_ratchet.cpp b/tests/test_ratchet.cpp
index fb60ba9..0408429 100644
--- a/tests/test_ratchet.cpp
+++ b/tests/test_ratchet.cpp
@@ -16,6 +16,7 @@
 #include "olm/cipher.h"
 #include "unittest.hh"
 
+#include <vector>
 
 int main() {
 
@@ -57,23 +58,23 @@ std::size_t encrypt_length, decrypt_length;
     random_length = alice.encrypt_random_length();
     assert_equals(std::size_t(0), random_length);
 
-    std::uint8_t message[message_length];
+    std::vector<std::uint8_t> message(message_length);
 
     encrypt_length = alice.encrypt(
         plaintext, plaintext_length,
         NULL, 0,
-        message, message_length
+        message.data(), message_length
     );
     assert_equals(message_length, encrypt_length);
 
-    output_length = bob.decrypt_max_plaintext_length(message, message_length);
-    std::uint8_t output[output_length];
+    output_length = bob.decrypt_max_plaintext_length(message.data(), message_length);
+    std::vector<std::uint8_t> output(output_length);
     decrypt_length = bob.decrypt(
-        message, message_length,
-        output, output_length
+        message.data(), message_length,
+        output.data(), output_length
     );
     assert_equals(plaintext_length, decrypt_length);
-    assert_equals(plaintext, output, decrypt_length);
+    assert_equals(plaintext, output.data(), decrypt_length);
 }
 
 
@@ -83,24 +84,24 @@ std::size_t encrypt_length, decrypt_length;
     random_length = bob.encrypt_random_length();
     assert_equals(std::size_t(32), random_length);
 
-    std::uint8_t message[message_length];
+    std::vector<std::uint8_t> message(message_length);
     std::uint8_t random[] = "This is a random 32 byte string.";
 
     encrypt_length = bob.encrypt(
         plaintext, plaintext_length,
         random, 32,
-        message, message_length
+        message.data(), message_length
     );
     assert_equals(message_length, encrypt_length);
 
-    output_length = alice.decrypt_max_plaintext_length(message, message_length);
-    std::uint8_t output[output_length];
+    output_length = alice.decrypt_max_plaintext_length(message.data(), message_length);
+    std::vector<std::uint8_t> output(output_length);
     decrypt_length = alice.decrypt(
-        message, message_length,
-        output, output_length
+        message.data(), message_length,
+        output.data(), output_length
     );
     assert_equals(plaintext_length, decrypt_length);
-    assert_equals(plaintext, output, decrypt_length);
+    assert_equals(plaintext, output.data(), decrypt_length);
 }
 
 } /* Send/receive message test case */
@@ -130,12 +131,12 @@ std::size_t encrypt_length, decrypt_length;
     random_length = alice.encrypt_random_length();
     assert_equals(std::size_t(0), random_length);
 
-    std::uint8_t message_1[message_1_length];
+    std::vector<std::uint8_t> message_1(message_1_length);
     std::uint8_t random[] = "This is a random 32 byte string.";
     encrypt_length = alice.encrypt(
         plaintext_1, plaintext_1_length,
         random, 32,
-        message_1, message_1_length
+        message_1.data(), message_1_length
     );
     assert_equals(message_1_length, encrypt_length);
 
@@ -143,36 +144,36 @@ std::size_t encrypt_length, decrypt_length;
     random_length = alice.encrypt_random_length();
     assert_equals(std::size_t(0), random_length);
 
-    std::uint8_t message_2[message_2_length];
+    std::vector<std::uint8_t> message_2(message_2_length);
     encrypt_length = alice.encrypt(
         plaintext_2, plaintext_2_length,
         NULL, 0,
-        message_2, message_2_length
+        message_2.data(), message_2_length
     );
     assert_equals(message_2_length, encrypt_length);
 
     output_length = bob.decrypt_max_plaintext_length(
-        message_2, message_2_length
+        message_2.data(), message_2_length
     );
-    std::uint8_t output_1[output_length];
+    std::vector<std::uint8_t> output_1(output_length);
     decrypt_length = bob.decrypt(
-        message_2, message_2_length,
-        output_1, output_length
+        message_2.data(), message_2_length,
+        output_1.data(), output_length
     );
     assert_equals(plaintext_2_length, decrypt_length);
-    assert_equals(plaintext_2, output_1, decrypt_length);
+    assert_equals(plaintext_2, output_1.data(), decrypt_length);
 
     output_length = bob.decrypt_max_plaintext_length(
-        message_1, message_1_length
+        message_1.data(), message_1_length
     );
-    std::uint8_t output_2[output_length];
+    std::vector<std::uint8_t> output_2(output_length);
     decrypt_length = bob.decrypt(
-        message_1, message_1_length,
-        output_2, output_length
+        message_1.data(), message_1_length,
+        output_2.data(), output_length
     );
 
     assert_equals(plaintext_1_length, decrypt_length);
-    assert_equals(plaintext_1, output_2, decrypt_length);
+    assert_equals(plaintext_1, output_2.data(), decrypt_length);
 }
 
 } /* Out of order test case */
@@ -193,24 +194,24 @@ std::uint8_t random[] = "This is a random 32 byte string";
 
 for (unsigned i = 0; i < 8; ++i) {
 {
-    std::uint8_t msg[alice.encrypt_output_length(sizeof(plaintext))];
+    std::vector<std::uint8_t> msg(alice.encrypt_output_length(sizeof(plaintext)));
     alice.encrypt(
-        plaintext, 15, random, 32, msg, sizeof(msg)
+        plaintext, 15, random, 32, msg.data(), msg.size()
     );
-    std::uint8_t output[bob.decrypt_max_plaintext_length(msg, sizeof(msg))];
+    std::vector<std::uint8_t> output(bob.decrypt_max_plaintext_length(msg.data(), msg.size()));
     assert_equals(
-        std::size_t(15), bob.decrypt(msg, sizeof(msg), output, sizeof(output))
+        std::size_t(15), bob.decrypt(msg.data(), msg.size(), output.data(), output.size())
     );
 }
 random[31]++;
 {
-    std::uint8_t msg[bob.encrypt_output_length(sizeof(plaintext))];
+    std::vector<std::uint8_t> msg(bob.encrypt_output_length(sizeof(plaintext)));
     bob.encrypt(
-        plaintext, 15, random, 32, msg, sizeof(msg)
+        plaintext, 15, random, 32, msg.data(), msg.size()
     );
-    std::uint8_t output[alice.decrypt_max_plaintext_length(msg, sizeof(msg))];
+    std::vector<std::uint8_t> output(alice.decrypt_max_plaintext_length(msg.data(), msg.size()));
     assert_equals(
-        std::size_t(15), alice.decrypt(msg, sizeof(msg), output, sizeof(output))
+        std::size_t(15), alice.decrypt(msg.data(), msg.size(), output.data(), output.size())
     );
 }
 random[31]++;