diff --git a/src/Makefile b/src/Makefile
index 4a5a945..2c9d51b 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -12,7 +12,7 @@ VERSION := $(shell \
 DEPDIR := .deps
 DEPFLAGS = -MT $@ -MMD -MP -MF $(DEPDIR)/$*.d
 
-CFLAGS := -Wall -Werror -ggdb -fno-omit-frame-pointer -O2 -D_FORTIFY_SOURCE=2
+CFLAGS += -Wall -Werror -ggdb -fno-omit-frame-pointer -O2 -D_FORTIFY_SOURCE=2
 CFLAGS += -DVERSION=\"$(VERSION)\"
 CFLAGS += -Wno-error=deprecated-declarations