diff --git a/Makefile b/Makefile
index 0ab5707..32b8823 100644
--- a/Makefile
+++ b/Makefile
@@ -31,7 +31,7 @@ WITH_SDL ?= yes
 
 OPTIM ?= 2
 
-CFLAGS = -std=c11 -g -O$(OPTIM) -I./src/ -D_GNU_SOURCE=1 -DVERSION_MAJOR=$(VERSION_MAJOR) -DVERSION_MINOR=$(VERSION_MINOR) -DPATCHLEVEL=$(PATCHLEVEL)
+CFLAGS += -std=c11 -g -O$(OPTIM) -I./src/ -D_GNU_SOURCE=1 -DVERSION_MAJOR=$(VERSION_MAJOR) -DVERSION_MINOR=$(VERSION_MINOR) -DPATCHLEVEL=$(PATCHLEVEL)
 LIBS = -lm
 
 ### lua