diff --git a/debian/rules b/debian/rules
index 5f1f3d6..eb37626 100755
--- a/debian/rules
+++ b/debian/rules
@@ -5,7 +5,7 @@ export DH_VERBOSE=1
 VERSION=$(shell grep PROFTPD_VERSION_TEXT /usr/include/proftpd/version.h|cut -d\" -f2)
 MODULE_NAME=mod_proxy_protocol
 DEBNAME=proftpd-mod-proxy-protocol
-CFLAGS="$CFLAGS -Wno-implicit-function-declaration"
+CFLAGS := -Wno-implicit-function-declaration
 
 %:
 	dh $@ --without python-support