--- a/sys/netgraph7/ng_source.c
+++ b/sys/netgraph7/ng_source.c
@@ ng_source_rcvdata @@
 	/* Enqueue packet. */
-	/* XXX should we check IF_QFULL() ? */
-	_IF_ENQUEUE(&sc->snd_queue, m);
+	if (IF_QFULL(&sc->snd_queue)) {
+		NG_FREE_M(m);
+		return (ENOBUFS);
+	}
+	_IF_ENQUEUE(&sc->snd_queue, m);