diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -1529,7 +1529,7 @@
 	struct mbuf *mfree;
 	struct tcpopt to;
 	int tfo_syn;
-	u_int maxseg;
+	u_int maxseg = 0;
 
 	thflags = tcp_get_flags(th);
 	tp->sackhint.last_sack_ack = 0;
@@ -2596,7 +2596,7 @@
 					if (V_tcp_do_prr &&
 					    IN_FASTRECOVERY(tp->t_flags) &&
 					    (tp->t_flags & TF_SACK_PERMIT)) {
-						tcp_do_prr_ack(tp, th, &to, sack_changed);
+						tcp_do_prr_ack(tp, th, &to, sack_changed, &maxseg);
 					} else if (tcp_is_sack_recovery(tp, &to) &&
 					    IN_FASTRECOVERY(tp->t_flags)) {
 						int awnd;
@@ -2805,11 +2805,12 @@
 					if (V_tcp_do_prr && to.to_flags & TOF_SACK) {
 						tcp_timer_activate(tp, TT_REXMT, 0);
 						tp->t_rtttime = 0;
-						tcp_do_prr_ack(tp, th, &to, sack_changed);
+						tcp_do_prr_ack(tp, th, &to, sack_changed,
+						    &maxseg);
 						tp->t_flags |= TF_ACKNOW;
 						(void) tcp_output(tp);
 					} else
-						tcp_sack_partialack(tp, th);
+						tcp_sack_partialack(tp, th, &maxseg);
 				else
 					tcp_newreno_partial_ack(tp, th);
 			} else
@@ -2823,7 +2824,7 @@
 					 * During ECN cwnd reduction
 					 * always use PRR-SSRB
 					 */
-					tcp_do_prr_ack(tp, th, &to, SACK_CHANGE);
+					tcp_do_prr_ack(tp, th, &to, SACK_CHANGE, &maxseg);
 					(void) tcp_output(tp);
 				}
 			} else
@@ -3946,13 +3947,15 @@
 }
 
 void
-tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to, sackstatus_t sack_changed)
+tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to, sackstatus_t sack_changed, u_int *maxseg)
 {
 	int snd_cnt = 0, limit = 0, del_data = 0, pipe = 0;
-	int maxseg = tcp_maxseg(tp);
 
 	INP_WLOCK_ASSERT(tptoinpcb(tp));
 
+	if (*maxseg == 0) {
+		*maxseg = tcp_maxseg(tp);
+	}
 	/*
 	 * Compute the amount of data that this ACK is indicating
 	 * (del_data) and an estimate of how many bytes are in the
@@ -3968,11 +3971,11 @@
 			pipe = (tp->snd_nxt - tp->snd_fack) +
 				tp->sackhint.sack_bytes_rexmit;
 	} else {
-		if (tp->sackhint.prr_delivered < (tcprexmtthresh * maxseg +
+		if (tp->sackhint.prr_delivered < (tcprexmtthresh * *maxseg +
 					     tp->snd_recover - tp->snd_una))
-			del_data = maxseg;
+			del_data = *maxseg;
 		pipe = imax(0, tp->snd_max - tp->snd_una -
-			    imin(INT_MAX / 65536, tp->t_dupacks) * maxseg);
+			    imin(INT_MAX / 65536, tp->t_dupacks) * *maxseg);
 	}
 	tp->sackhint.prr_delivered += del_data;
 	/*
@@ -3984,7 +3987,7 @@
 			    imax(1, tp->snd_nxt - tp->snd_una);
 		snd_cnt = howmany((long)tp->sackhint.prr_delivered *
 			    tp->snd_ssthresh, tp->sackhint.recover_fs) -
-			    tp->sackhint.prr_out + maxseg - 1;
+			    tp->sackhint.prr_out + *maxseg - 1;
 	} else {
 		/*
 		 * PRR 6937bis heuristic:
@@ -4002,10 +4005,10 @@
 		else
 			limit = imax(tp->sackhint.prr_delivered -
 				    tp->sackhint.prr_out, del_data) +
-				    maxseg;
+				    *maxseg;
 		snd_cnt = imin((tp->snd_ssthresh - pipe), limit);
 	}
-	snd_cnt = imax(snd_cnt, 0) / maxseg;
+	snd_cnt = imax(snd_cnt, 0) / *maxseg;
 	/*
 	 * Send snd_cnt new data into the network in response to this ack.
 	 * If there is going to be a SACK retransmission, adjust snd_cwnd
@@ -4015,14 +4018,14 @@
 		if (tcp_is_sack_recovery(tp, to)) {
 			tp->snd_cwnd = tp->snd_nxt - tp->snd_recover +
 					    tp->sackhint.sack_bytes_rexmit +
-					    (snd_cnt * maxseg);
+					    (snd_cnt * *maxseg);
 		} else {
 			tp->snd_cwnd = (tp->snd_max - tp->snd_una) +
-					    (snd_cnt * maxseg);
+					    (snd_cnt * *maxseg);
 		}
 	} else if (IN_CONGRECOVERY(tp->t_flags))
-		tp->snd_cwnd = pipe - del_data + (snd_cnt * maxseg);
-	tp->snd_cwnd = imax(maxseg, tp->snd_cwnd);
+		tp->snd_cwnd = pipe - del_data + (snd_cnt * *maxseg);
+	tp->snd_cwnd = imax(*maxseg, tp->snd_cwnd);
 }
 
 /*
diff --git a/sys/netinet/tcp_sack.c b/sys/netinet/tcp_sack.c
--- a/sys/netinet/tcp_sack.c
+++ b/sys/netinet/tcp_sack.c
@@ -936,20 +936,23 @@
  * the midst of sack recovery.
  */
 void
-tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
+tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th, u_int *maxseg)
 {
 	struct sackhole *temp;
 	int num_segs = 1;
-	u_int maxseg = tcp_maxseg(tp);
 
 	INP_WLOCK_ASSERT(tptoinpcb(tp));
+
+	if (*maxseg == 0) {
+		*maxseg = tcp_maxseg(tp);
+	}
 	tcp_timer_activate(tp, TT_REXMT, 0);
 	tp->t_rtttime = 0;
 	/* Send one or 2 segments based on how much new data was acked. */
-	if ((BYTES_THIS_ACK(tp, th) / maxseg) >= 2)
+	if ((BYTES_THIS_ACK(tp, th) / *maxseg) >= 2)
 		num_segs = 2;
 	tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
-	    (tp->snd_nxt - tp->snd_recover) + num_segs * maxseg);
+	    (tp->snd_nxt - tp->snd_recover) + num_segs * *maxseg);
 	if (tp->snd_cwnd > tp->snd_ssthresh)
 		tp->snd_cwnd = tp->snd_ssthresh;
 	tp->t_flags |= TF_ACKNOW;
@@ -986,7 +989,7 @@
 		if (th->th_ack != highdata) {
 			tp->snd_fack = th->th_ack;
 			if ((temp = tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
-			    highdata - maxseg), highdata, NULL)) != NULL)
+			    highdata - *maxseg), highdata, NULL)) != NULL)
 				tp->sackhint.hole_bytes += temp->end -
 								temp->start;
 		}
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -1486,9 +1486,9 @@
 void	 tcp_clean_sackreport(struct tcpcb *tp);
 void	 tcp_sack_adjust(struct tcpcb *tp);
 struct sackhole *tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt);
-void	 tcp_do_prr_ack(struct tcpcb *, struct tcphdr *, struct tcpopt *, sackstatus_t);
+void	 tcp_do_prr_ack(struct tcpcb *, struct tcphdr *, struct tcpopt *, sackstatus_t, u_int *);
 void	 tcp_lost_retransmission(struct tcpcb *, struct tcphdr *);
-void	 tcp_sack_partialack(struct tcpcb *, struct tcphdr *);
+void	 tcp_sack_partialack(struct tcpcb *, struct tcphdr *, u_int *);
 void	 tcp_resend_sackholes(struct tcpcb *tp);
 void	 tcp_free_sackholes(struct tcpcb *tp);
 void	 tcp_sack_lost_retransmission(struct tcpcb *, struct tcphdr *);