diff --git a/Makefile b/Makefile
index ff620a8..01b6bf9 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,7 @@
 CC	?= gcc
 STRIP ?= strip
-CFLAGS = -std=c99 -Os
+CFLAGS ?= -Os
+CFLAGS += -std=c99
 LDFLAGS = -lxcb -lxcb-xinerama -lxcb-randr
 CFDEBUG = -g3 -pedantic -Wall -Wunused-parameter -Wlong-long\
 		  -Wsign-conversion -Wconversion -Wimplicit-function-declaration