--- Makefile.orig
+++ Makefile
@@ -2,7 +2,7 @@
 VERSION = $(shell git describe || cat VERSION)
 
 CPPFLAGS += -D_POSIX_C_SOURCE=200112L -DVERSION=\"$(VERSION)\"
-CFLAGS   += -std=c99 -pedantic -Wall -Wextra
+override CFLAGS   += -std=c99 -pedantic -Wall -Wextra
 LDLIBS    = -lxcb -lxcb-icccm -lxcb-ewmh -lxcb-xtest
 
 PREFIX    ?= /usr/local
