Index: sys/netpfil/pf/pf.c
===================================================================
--- sys/netpfil/pf/pf.c	(revision 277815)
+++ sys/netpfil/pf/pf.c	(working copy)
@@ -4199,7 +4199,7 @@
 			    TH_SYN|TH_ACK, 0, (*state)->src.mss, 0, 1, 0, NULL);
 			REASON_SET(reason, PFRES_SYNPROXY);
 			return (PF_SYNPROXY_DROP);
-		} else if (!(th->th_flags & TH_ACK) ||
+		} else if ((th->th_flags & (TH_ACK|TH_RST|TH_FIN)) != TH_ACK ||
 		    (ntohl(th->th_ack) != (*state)->src.seqhi + 1) ||
 		    (ntohl(th->th_seq) != (*state)->src.seqlo + 1)) {
 			REASON_SET(reason, PFRES_SYNPROXY);