diff --git a/GNUmakefile.gcc_plugin b/GNUmakefile.gcc_plugin
index 3f658a47..ee211c24 100644
--- a/GNUmakefile.gcc_plugin
+++ b/GNUmakefile.gcc_plugin
@@ -67,12 +67,12 @@ ifeq "$(shell echo '$(HASH)include <sys/ipc.h>@$(HASH)include <sys/shm.h>@int ma
 	SHMAT_OK=1
 else
 	SHMAT_OK=0
-	override CFLAGS += -DUSEMMAP=1
+	override CFLAGS_SAFE += -DUSEMMAP=1
 endif
 
 ifeq "$(TEST_MMAP)" "1"
 	SHMAT_OK=0
-	override CFLAGS += -DUSEMMAP=1
+	override CFLAGS_SAFE += -DUSEMMAP=1
 endif
 
 ifneq "$(shell uname -s)" "Haiku"