diff --git a/sys/conf/kern.post.mk b/sys/conf/kern.post.mk
index 4cb60c002b62..32ec5b1b445c 100644
--- a/sys/conf/kern.post.mk
+++ b/sys/conf/kern.post.mk
@@ -65,6 +65,10 @@ OSRELDATE!=	awk '/^\#define[[:space:]]*__FreeBSD_version/ { print $$3 }' \
 # Keep the related ports builds in the obj directory so that they are only rebuilt once per kernel build
 WRKDIRPREFIX?=	${MAKEOBJDIRPREFIX}${SRC_BASE}/sys/${KERNCONF}
 PORTSMODULESENV=\
+	env \
+	-u CC \
+	-u CXX \
+	-u CPP \
 	PATH=${PATH}:${LOCALBASE}/bin:${LOCALBASE}/sbin \
 	SRC_BASE=${SRC_BASE} \
 	OSVERSION=${OSRELDATE} \