diff --git a/Makefile b/Makefile
index 4f5adf2..d960e9f 100644
--- a/Makefile
+++ b/Makefile
@@ -2,13 +2,14 @@
 
 # Make sure that the build directory exists.
 # We can't check the build directory into git because it is empty.
-BUILD_DIR := $(shell mkdir -p build; echo build)
-OPTIMIZE_FLAGS ?= -g -O3
-TEST_OPTIMIZE_FLAGS ?= -g -O0
+BUILD_DIR := $(shell mkdir -p build/release build/debug build/javascript build/tests; echo build)
+RELEASE_OPTIMIZE_FLAGS ?= -g -O3
+DEBUG_OPTIMIZE_FLAGS ?= -g -O0
 JS_OPTIMIZE_FLAGS ?= -O3
 CC = gcc
 EMCC = emcc
-TARGET := $(BUILD_DIR)/libolm.so
+RELEASE_TARGET := $(BUILD_DIR)/libolm.so
+DEBUG_TARGET := $(BUILD_DIR)/libolm_debug.so
 JS_TARGET := javascript/olm.js
 
 JS_EXPORTED_FUNCTIONS := javascript/exported_functions.json
@@ -16,13 +17,15 @@ JS_EXPORTED_FUNCTIONS := javascript/exported_functions.json
 PUBLIC_HEADERS := include/olm/olm.hh
 
 SOURCES := $(wildcard src/*.cpp) $(wildcard src/*.c)
-OBJECTS := $(patsubst src/%,$(BUILD_DIR)/%,$(patsubst %.c,%.o,$(patsubst %.cpp,%.o,$(SOURCES))))
+RELEASE_OBJECTS := $(patsubst src/%,$(BUILD_DIR)/release/%,$(patsubst %.c,%.o,$(patsubst %.cpp,%.o,$(SOURCES))))
+DEBUG_OBJECTS := $(patsubst src/%,$(BUILD_DIR)/debug/%,$(patsubst %.c,%.o,$(patsubst %.cpp,%.o,$(SOURCES))))
 TEST_SOURCES := $(wildcard tests/test_*.cpp) $(wildcard tests/test_*.c)
-TEST_BINARIES := $(patsubst tests/%,$(BUILD_DIR)/%,$(patsubst %.c,%,$(patsubst %.cpp,%,$(TEST_SOURCES))))
-JS_OBJECTS := $(patsubst %.o,%.js.bc,$(OBJECTS))
+TEST_BINARIES := $(patsubst tests/%,$(BUILD_DIR)/tests/%,$(patsubst %.c,%,$(patsubst %.cpp,%,$(TEST_SOURCES))))
+JS_OBJECTS := $(patsubst src/%,$(BUILD_DIR)/javascript/%,$(patsubst %.c,%.js.bc,$(patsubst %.cpp,%.js.bc,$(SOURCES))))
 JS_PRE := $(wildcard javascript/*pre.js)
 JS_POST := $(wildcard javascript/*post.js)
 
+
 CPPFLAGS += -Iinclude -Ilib
 CFLAGS += -Wall -std=c89 -fPIC
 CXXFLAGS += -Wall -std=c++11 -fPIC
@@ -42,9 +45,13 @@ CPPFLAGS += -MMD
 
 ### per-target variables
 
-$(OBJECTS): CFLAGS += $(OPTIMIZE_FLAGS)
-$(OBJECTS): CXXFLAGS += $(OPTIMIZE_FLAGS)
-$(TARGET): LDFLAGS += $(OPTIMIZE_FLAGS)
+$(RELEASE_OBJECTS): CFLAGS += $(RELEASE_OPTIMIZE_FLAGS)
+$(RELEASE_OBJECTS): CXXFLAGS += $(RELEASE_OPTIMIZE_FLAGS)
+$(RELEASE_TARGET): LDFLAGS += $(RELEASE_OPTIMIZE_FLAGS)
+
+$(DEBUG_OBJECTS): CFLAGS += $(DEBUG_OPTIMIZE_FLAGS)
+$(DEBUG_OBJECTS): CXXFLAGS += $(DEBUG_OPTIMIZE_FLAGS)
+$(DEBUG_TARGET): LDFLAGS += $(DEBUG_OPTIMIZE_FLAGS)
 
 $(TEST_BINARIES): CPPFLAGS += -Itests/include
 $(TEST_BINARIES): LDFLAGS += $(TEST_OPTIMIZE_FLAGS) -L$(BUILD_DIR)
@@ -55,25 +62,35 @@ $(JS_TARGET): LDFLAGS += $(JS_OPTIMIZE_FLAGS)
 
 ### top-level targets
 
-lib: $(TARGET)
+lib: $(RELEASE_TARGET)
 .PHONY: lib
 
-$(TARGET): $(OBJECTS)
+$(RELEASE_TARGET): $(RELEASE_OBJECTS)
 	$(CXX) $(LDFLAGS) --shared -fPIC \
-	    -Wl,--version-script,version_script.ver \
-            $(OUTPUT_OPTION) $(OBJECTS)
+            -Wl,--version-script,version_script.ver \
+            $(OUTPUT_OPTION) $(RELEASE_OBJECTS)
+
+debug: $(DEBUG_TARGET)
+.PHONY: debug
+
+$(DEBUG_TARGET): $(DEBUG_OBJECTS)
+	$(CXX) $(LDFLAGS) --shared -fPIC \
+            -Wl,--version-script,version_script.ver \
+            $(OUTPUT_OPTION) $(DEBUG_OBJECTS)
+
 
 js: $(JS_TARGET)
 .PHONY: js
 
 $(JS_TARGET): $(JS_OBJECTS) $(JS_PRE) $(JS_POST) $(JS_EXPORTED_FUNCTIONS)
 	$(EMCC_LINK) \
-	       --pre-js $(JS_PRE) --post-js $(JS_POST) \
-	       -s "EXPORTED_FUNCTIONS=@$(JS_EXPORTED_FUNCTIONS)" \
+               --pre-js $(JS_PRE) --post-js $(JS_POST) \
+               -s "EXPORTED_FUNCTIONS=@$(JS_EXPORTED_FUNCTIONS)" \
                $(JS_OBJECTS) -o $@
 
 clean:;
-	rm -rf $(OBJECTS) $(OBJECTS:.o=.d) \
+	rm -rf $(RELEASE_OBJECTS) $(RELEASE_OBJECTS:.o=.d) \
+               $(DEBUG_OBJECTS) $(DEBUG_OBJECTS:.o=.d) \
                $(TEST_BINARIES) $(TEST_BINARIES:=.d) \
                $(JS_OBJECTS) $(JS_OBJECTS:=.d) $(JS_TARGET) \
                $(JS_EXPORTED_FUNCTIONS) \
@@ -91,31 +108,38 @@ $(JS_EXPORTED_FUNCTIONS): $(PUBLIC_HEADERS)
 	perl -MJSON -ne '/(olm_[^( ]*)\(/ && push @f, "_$$1"; END { print encode_json \@f }' $^ > $@.tmp
 	mv $@.tmp $@
 
-all: test js lib
+all: test js lib debug
 .PHONY: lib
 
 ### rules for building objects
-$(BUILD_DIR)/%.o: src/%.c
+$(BUILD_DIR)/release/%.o: src/%.c
 	$(COMPILE.c) $(OUTPUT_OPTION) $<
 
-$(BUILD_DIR)/%.o: src/%.cpp
+$(BUILD_DIR)/release/%.o: src/%.cpp
 	$(COMPILE.cc) $(OUTPUT_OPTION) $<
 
-$(BUILD_DIR)/%.js.bc: src/%.c
+$(BUILD_DIR)/debug/%.o: src/%.c
+	$(COMPILE.c) $(OUTPUT_OPTION) $<
+
+$(BUILD_DIR)/debug/%.o: src/%.cpp
+	$(COMPILE.cc) $(OUTPUT_OPTION) $<
+
+$(BUILD_DIR)/javascript/%.js.bc: src/%.c
 	$(EMCC.c) $(OUTPUT_OPTION) $<
 
-$(BUILD_DIR)/%.js.bc: src/%.cpp
+$(BUILD_DIR)/javascript/%.js.bc: src/%.cpp
 	$(EMCC.cc) $(OUTPUT_OPTION) $<
 
-$(BUILD_DIR)/%: tests/%.c $(OBJECTS)
-	$(LINK.c) $< $(OBJECTS) $(LOADLIBES) $(LDLIBS) -o $@
+$(BUILD_DIR)/tests/%: tests/%.c $(DEBUG_OBJECTS)
+	$(LINK.c) $^ $(LOADLIBES) $(LDLIBS) -o $@
 
-$(BUILD_DIR)/%: tests/%.cpp $(OBJECTS)
-	$(LINK.cc) $< $(OBJECTS) $(LOADLIBES) $(LDLIBS) -o $@
+$(BUILD_DIR)/tests/%: tests/%.cpp $(DEBUG_OBJECTS)
+	$(LINK.cc) $^ $(LOADLIBES) $(LDLIBS) -o $@
 
 
 ### dependencies
 
--include $(OBJECTS:.o=.d)
+-include $(RELEASE_OBJECTS:.o=.d)
+-include $(DEBUG_OBJECTS:.o=.d)
 -include $(JS_OBJECTS:.bc=.d)
 -include $(TEST_BINARIES:=.d)