diff --git a/sys/netinet/tcp_syncache.c b/sys/netinet/tcp_syncache.c
index e19f0956fad7..88b2c5e7cc64 100644
--- a/sys/netinet/tcp_syncache.c
+++ b/sys/netinet/tcp_syncache.c
@@ -906,11 +906,14 @@ syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 		goto failed;
 	}
 	/*
-	 * The SEQ must match the received initial receive sequence
-	 * number + 1 (the SYN) because we didn't ACK any data that
-	 * may have come with the SYN.
+	 * The SEQ must fall in the window starting a the received initial receive 
+	 * sequence number + 1 (the SYN).
 	 */
-	if (th->th_seq != sc->sc_irs + 1 && !TOEPCB_ISSET(sc)) {
+
+	if ((SEQ_LEQ(th->th_seq, sc->sc_irs) ||
+	    SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd )) &&
+	    !TOEPCB_ISSET(sc))
+	{
 		if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 			log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
 			    "rejected\n", s, __func__, th->th_seq, sc->sc_irs);