Index: sys/netgraph/ng_source.c
===================================================================
--- sys/netgraph/ng_source.c
+++ sys/netgraph/ng_source.c
@@ -683,8 +683,8 @@
 static int
 ng_source_start(sc_p sc, uint64_t packets)
 {
-	if (sc->output_ifp == NULL) {
-		printf("ng_source: start without iface configured\n");
+	if (sc->output_ifp == NULL && sc->stats.maxPps == 0) {
+		printf("ng_source: start without iface or pps configured\n");
 		return (ENXIO);
 	}