--- a/makefile.inc
+++ b/makefile.inc
@@ -436,8 +436,8 @@ bin-debug :
 	$(MAKE) prepare BUILD_DIR=build-obj/debug/$(EXE)
 	$(MAKE) -C build-obj/debug/$(EXE) $(EXE) \
 		DP_MAKE_TARGET=$(DP_MAKE_TARGET) DP_SOUND_API=$(DP_SOUND_API) \
-		CFLAGS='$(CFLAGS_COMMON) $(CFLAGS_FEATURES) $(CFLAGS_EXTRA) $(CFLAGS_DEBUG) $(OPTIM_DEBUG)'\
-		LDFLAGS='$(LDFLAGS_DEBUG) $(LDFLAGS_COMMON)' LEVEL=2
+		CFLAGS+='$(CFLAGS_COMMON) $(CFLAGS_FEATURES) $(CFLAGS_EXTRA) $(CFLAGS_DEBUG) $(OPTIM_DEBUG)'\
+		LDFLAGS+='$(LDFLAGS_DEBUG) $(LDFLAGS_COMMON)' LEVEL=2
 
 bin-profile :
 	$(CHECKLEVEL1)
@@ -446,8 +446,8 @@ bin-profile :
 	$(MAKE) prepare BUILD_DIR=build-obj/profile/$(EXE)
 	$(MAKE) -C build-obj/profile/$(EXE) $(EXE) \
 		DP_MAKE_TARGET=$(DP_MAKE_TARGET) DP_SOUND_API=$(DP_SOUND_API) \
-		CFLAGS='$(CFLAGS_COMMON) $(CFLAGS_FEATURES) $(CFLAGS_EXTRA) $(CFLAGS_PROFILE) $(OPTIM_RELEASE)'\
-		LDFLAGS='$(LDFLAGS_PROFILE) $(LDFLAGS_COMMON)' LEVEL=2
+		CFLAGS+='$(CFLAGS_COMMON) $(CFLAGS_FEATURES) $(CFLAGS_EXTRA) $(CFLAGS_PROFILE) $(OPTIM_RELEASE)'\
+		LDFLAGS+='$(LDFLAGS_PROFILE) $(LDFLAGS_COMMON)' LEVEL=2
 
 bin-release :
 	$(CHECKLEVEL1)
@@ -456,8 +456,8 @@ bin-release :
 	$(MAKE) prepare BUILD_DIR=build-obj/release/$(EXE)
 	$(MAKE) -C build-obj/release/$(EXE) $(EXE) \
 		DP_MAKE_TARGET=$(DP_MAKE_TARGET) DP_SOUND_API=$(DP_SOUND_API) \
-		CFLAGS='$(CFLAGS_COMMON) $(CFLAGS_FEATURES) $(CFLAGS_EXTRA) $(CFLAGS_RELEASE) $(OPTIM_RELEASE)'\
-		LDFLAGS='$(LDFLAGS_RELEASE) $(LDFLAGS_COMMON)' LEVEL=2
+		CFLAGS+='$(CFLAGS_COMMON) $(CFLAGS_FEATURES) $(CFLAGS_EXTRA) $(CFLAGS_RELEASE) $(OPTIM_RELEASE)'\
+		LDFLAGS+='$(LDFLAGS_RELEASE) $(LDFLAGS_COMMON)' LEVEL=2
 	$(STRIP) $(EXE)
 
 bin-release-profile :
@@ -467,8 +467,8 @@ bin-release-profile :
 	$(MAKE) prepare BUILD_DIR=build-obj/release-profile/$(EXE)
 	$(MAKE) -C build-obj/release-profile/$(EXE) $(EXE) \
 		DP_MAKE_TARGET=$(DP_MAKE_TARGET) DP_SOUND_API=$(DP_SOUND_API) \
-		CFLAGS='$(CFLAGS_COMMON) $(CFLAGS_FEATURES) $(CFLAGS_EXTRA) $(CFLAGS_RELEASE_PROFILE) $(OPTIM_RELEASE)'\
-		LDFLAGS='$(LDFLAGS_RELEASE) $(LDFLAGS_COMMON)' LEVEL=2
+		CFLAGS+='$(CFLAGS_COMMON) $(CFLAGS_FEATURES) $(CFLAGS_EXTRA) $(CFLAGS_RELEASE_PROFILE) $(OPTIM_RELEASE)'\
+		LDFLAGS+='$(LDFLAGS_RELEASE) $(LDFLAGS_COMMON)' LEVEL=2
 	$(STRIP) $(EXE)
 
 prepare :