Index: sys/netinet/tcp_syncache.c
===================================================================
--- sys/netinet/tcp_syncache.c
+++ sys/netinet/tcp_syncache.c
@@ -1521,6 +1521,9 @@
 	sc->sc_todctx = todctx;
 #endif
 	sc->sc_irs = th->th_seq;
+	KASSERT(is_random_seeded(), ("%s: syncache_init() already relies on "
+	    "arc4random being available, so it must be here as well.",
+	    __func__));
 	sc->sc_iss = arc4random();
 	sc->sc_flags = 0;
 	sc->sc_flowlabel = 0;