diff --git a/sys/net/if_gif.c b/sys/net/if_gif.c
index 5fa7664780c..a4ac7243dbf 100644
--- a/sys/net/if_gif.c
+++ b/sys/net/if_gif.c
@@ -407,6 +407,9 @@ gif_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
 {
 	uint32_t af;
 
+	KASSERT(ifp->if_bridge == NULL,
+	    ("%s: unexpectedly called with bridge attached", __func__));
+
 	if (dst->sa_family == AF_UNSPEC)
 		memcpy(&af, dst->sa_data, sizeof(af));
 	else