diff --git a/sys/modules/ipfilter/Makefile b/sys/modules/ipfilter/Makefile
index 61778b7d3e5d..a98d29c45366 100644
--- a/sys/modules/ipfilter/Makefile
+++ b/sys/modules/ipfilter/Makefile
@@ -6,9 +6,11 @@ KMOD=	ipl
 SRCS=	mlfk_ipl.c ip_nat.c ip_frag.c ip_state.c ip_proxy.c ip_auth.c \
 	ip_log.c ip_fil.c fil.c
 
+CFLAGS+= -DUSE_INET6
 CFLAGS+=  -I${.CURDIR}/../../contrib/ipfilter
 CFLAGS+= -DIPFILTER=1 -DIPFILTER_LKM -DIPFILTER_LOG -DPFIL_HOOKS
 #
+# If you don't want IPv6 functionality remove -DUSE_INET6
 # If you don't want log functionality remove -DIPFILTER_LOG
 #