diff --git a/sys/netinet6/ip6_mroute.c b/sys/netinet6/ip6_mroute.c
--- a/sys/netinet6/ip6_mroute.c
+++ b/sys/netinet6/ip6_mroute.c
@@ -356,7 +356,7 @@
 {
 	struct mf6c *rt;
 
-	crit_enter();
+	ASSERT_NETISR0;
 	MF6CFIND(req->src.sin6_addr, req->grp.sin6_addr, rt);
 	crit_exit();
 	if (rt != NULL) {