Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -449,6 +449,8 @@
 	case CC_NDUPACK:
 		if (!IN_FASTRECOVERY(tp->t_flags)) {
 			tp->snd_recover = tp->snd_max;
+			if (__predict_false(tp->t_flags & TF_SENTFIN))
+				tp->snd_recover--;
 			if (tp->t_flags2 & TF2_ECN_PERMIT)
 				tp->t_flags2 |= TF2_ECN_SND_CWR;
 		}
@@ -463,6 +465,8 @@
 			EXIT_CONGRECOVERY(tp->t_flags);
 			TCPSTAT_INC(tcps_ecn_rcwnd);
 			tp->snd_recover = tp->snd_max + 1;
+			if (__predict_false(tp->t_flags & TF_SENTFIN))
+				tp->snd_recover -= 2;
 			if (tp->t_flags2 & TF2_ECN_PERMIT)
 				tp->t_flags2 |= TF2_ECN_SND_CWR;
 		}
@@ -485,6 +489,8 @@
 		if (tp->t_flags & TF_WASCRECOVERY)
 			ENTER_CONGRECOVERY(tp->t_flags);
 		tp->snd_nxt = tp->snd_max;
+		if (__predict_false(tp->t_flags & TF_SENTFIN))
+			tp->snd_nxt--;
 		tp->t_flags &= ~TF_PREVVALID;
 		tp->t_badrxtwin = 0;
 		break;
@@ -4014,7 +4020,12 @@
 int
 tcp_compute_pipe(struct tcpcb *tp)
 {
-	return (tp->snd_max - tp->snd_una +
+	int highdata;
+
+	highdata = tp->snd_max;
+	if (__predict_false(tp->t_flags & TF_SENTFIN))
+		highdata--;
+	return (highdata - tp->snd_una +
 		tp->sackhint.sack_bytes_rexmit -
 		tp->sackhint.sacked_bytes);
 }
Index: sys/netinet/tcp_sack.c
===================================================================
--- sys/netinet/tcp_sack.c
+++ sys/netinet/tcp_sack.c
@@ -543,6 +543,7 @@
 	struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
 	int i, j, num_sack_blks, sack_changed;
 	int delivered_data, left_edge_delta;
+	int highdata;
 
 	INP_WLOCK_ASSERT(tp->t_inpcb);
 
@@ -565,6 +566,9 @@
 	 * received new blocks from the other side.
 	 */
 	if (to->to_flags & TOF_SACK) {
+		highdata = tp->snd_max;
+		if (__predict_false(tp->t_flags & TF_SENTFIN))
+			highdata--;
 		for (i = 0; i < to->to_nsacks; i++) {
 			bcopy((to->to_sacks + i * TCPOLEN_SACK),
 			    &sack, sizeof(sack));
@@ -573,9 +577,9 @@
 			if (SEQ_GT(sack.end, sack.start) &&
 			    SEQ_GT(sack.start, tp->snd_una) &&
 			    SEQ_GT(sack.start, th_ack) &&
-			    SEQ_LT(sack.start, tp->snd_max) &&
+			    SEQ_LT(sack.start, highdata) &&
 			    SEQ_GT(sack.end, tp->snd_una) &&
-			    SEQ_LEQ(sack.end, tp->snd_max)) {
+			    SEQ_LEQ(sack.end, highdata)) {
 				sack_blocks[num_sack_blks++] = sack;
 			}
 		}
@@ -838,7 +842,7 @@
 		 * the ACK for a FIN is outstanding.
 		 */
 		tcp_seq highdata = tp->snd_max;
-		if (tp->t_flags & TF_SENTFIN)
+		if (__predict_false(tp->t_flags & TF_SENTFIN))
 			highdata--;
 		if (th->th_ack != highdata)
 			(void)tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
Index: sys/netinet/tcp_subr.c
===================================================================
--- sys/netinet/tcp_subr.c
+++ sys/netinet/tcp_subr.c
@@ -2933,6 +2933,8 @@
 	tp->snd_nxt = tp->snd_una;
 	tcp_free_sackholes(tp);
 	tp->snd_recover = tp->snd_max;
+	if (__predict_false(tp->t_flags & TF_SENTFIN))
+		tp->snd_recover--;
 	if (tp->t_flags & TF_SACK_PERMIT)
 		EXIT_FASTRECOVERY(tp->t_flags);
 	tp->t_fb->tfb_tcp_output(tp);
Index: sys/netinet/tcp_timer.c
===================================================================
--- sys/netinet/tcp_timer.c
+++ sys/netinet/tcp_timer.c
@@ -865,6 +865,8 @@
 	}
 	tp->snd_nxt = tp->snd_una;
 	tp->snd_recover = tp->snd_max;
+	if (__predict_false(tp->t_flags & TF_SENTFIN))
+		tp->snd_recover--;
 	/*
 	 * Force a segment to be sent.
 	 */