diff --git a/include/olm/inbound_group_session.h b/include/olm/inbound_group_session.h
index 49992b2..4798f27 100644
--- a/include/olm/inbound_group_session.h
+++ b/include/olm/inbound_group_session.h
@@ -95,8 +95,6 @@ size_t olm_unpickle_inbound_group_session(
  */
 size_t olm_init_inbound_group_session(
     OlmInboundGroupSession *session,
-    uint32_t message_index,
-
     /* base64-encoded keys */
     uint8_t const * session_key, size_t session_key_length
 );
diff --git a/javascript/olm_inbound_group_session.js b/javascript/olm_inbound_group_session.js
index 9722c31..7e07b01 100644
--- a/javascript/olm_inbound_group_session.js
+++ b/javascript/olm_inbound_group_session.js
@@ -52,12 +52,12 @@ InboundGroupSession.prototype['unpickle'] = restore_stack(function(key, pickle)
     );
 });
 
-InboundGroupSession.prototype['create'] = restore_stack(function(message_index, session_key) {
+InboundGroupSession.prototype['create'] = restore_stack(function(session_key) {
     var key_array = array_from_string(session_key);
     var key_buffer = stack(key_array);
 
     inbound_group_session_method(Module['_olm_init_inbound_group_session'])(
-        this.ptr, message_index, key_buffer, key_array.length
+        this.ptr, key_buffer, key_array.length
     );
 });
 
diff --git a/python/olm/inbound_group_session.py b/python/olm/inbound_group_session.py
index 6c01095..eb0422f 100644
--- a/python/olm/inbound_group_session.py
+++ b/python/olm/inbound_group_session.py
@@ -33,7 +33,7 @@ inbound_group_session_function(
 )
 
 inbound_group_session_function(
-    lib.olm_init_inbound_group_session, c_uint32, c_void_p, c_size_t
+    lib.olm_init_inbound_group_session, c_void_p, c_size_t
 )
 
 inbound_group_session_function(
@@ -66,10 +66,10 @@ class InboundGroupSession(object):
             self.ptr, key_buffer, len(key), pickle_buffer, len(pickle)
         )
 
-    def init(self, message_index, session_key):
+    def init(self, session_key):
         key_buffer = create_string_buffer(session_key)
         lib.olm_init_inbound_group_session(
-            self.ptr, message_index, key_buffer, len(session_key)
+            self.ptr, key_buffer, len(session_key)
         )
 
     def decrypt(self, message):
diff --git a/src/inbound_group_session.c b/src/inbound_group_session.c
index 82ff66f..b42ca86 100644
--- a/src/inbound_group_session.c
+++ b/src/inbound_group_session.c
@@ -113,7 +113,6 @@ static size_t _init_group_session_keys(
 
 size_t olm_init_inbound_group_session(
     OlmInboundGroupSession *session,
-    uint32_t message_index,
     const uint8_t * session_key, size_t session_key_length
 ) {
     uint8_t key_buf[SESSION_KEY_RAW_LENGTH];
diff --git a/tests/test_group_session.cpp b/tests/test_group_session.cpp
index ce889ad..3e11169 100644
--- a/tests/test_group_session.cpp
+++ b/tests/test_group_session.cpp
@@ -130,7 +130,7 @@ int main() {
         olm_inbound_group_session(inbound_session_memory);
 
     res = olm_init_inbound_group_session(
-        inbound_session, 0U, session_key, session_key_len);
+        inbound_session, session_key, session_key_len);
     assert_equals((size_t)0, res);
 
     /* decode the message */
@@ -172,7 +172,7 @@ int main() {
         olm_inbound_group_session(inbound_session_memory);
 
     size_t res = olm_init_inbound_group_session(
-        inbound_session, 0U, session_key, sizeof(session_key)-1
+        inbound_session, session_key, sizeof(session_key)-1
     );
     assert_equals((size_t)0, res);