Index: sys/netinet/cc/cc_newreno.c
===================================================================
--- sys/netinet/cc/cc_newreno.c
+++ sys/netinet/cc/cc_newreno.c
@@ -199,7 +199,7 @@
 static void
 newreno_after_idle(struct cc_var *ccv)
 {
-	int rw;
+	uint32_t rw;
 
 	/*
 	 * If we've been idle for more than one retransmit timeout the old
@@ -214,11 +214,7 @@
 	 *
 	 * See RFC5681 Section 4.1. "Restarting Idle Connections".
 	 */
-	if (V_tcp_do_rfc3390)
-		rw = min(4 * CCV(ccv, t_maxseg),
-		    max(2 * CCV(ccv, t_maxseg), 4380));
-	else
-		rw = CCV(ccv, t_maxseg) * 2;
+	rw = tcp_compute_initwnd(tcp_maxseg(ccv->ccvc.tcp));
 
 	CCV(ccv, snd_cwnd) = min(rw, CCV(ccv, snd_cwnd));
 }
Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -371,31 +371,14 @@
 	/*
 	 * Set the initial slow-start flight size.
 	 *
-	 * RFC5681 Section 3.1 specifies the default conservative values.
-	 * RFC3390 specifies slightly more aggressive values.
-	 * RFC6928 increases it to ten segments.
-	 * Support for user specified value for initial flight size.
-	 *
 	 * If a SYN or SYN/ACK was lost and retransmitted, we have to
 	 * reduce the initial CWND to one segment as congestion is likely
 	 * requiring us to be cautious.
 	 */
 	if (tp->snd_cwnd == 1)
 		tp->snd_cwnd = maxseg;		/* SYN(-ACK) lost */
-	else if (V_tcp_initcwnd_segments)
-		tp->snd_cwnd = min(V_tcp_initcwnd_segments * maxseg,
-		    max(2 * maxseg, V_tcp_initcwnd_segments * 1460));
-	else if (V_tcp_do_rfc3390)
-		tp->snd_cwnd = min(4 * maxseg, max(2 * maxseg, 4380));
-	else {
-		/* Per RFC5681 Section 3.1 */
-		if (maxseg > 2190)
-			tp->snd_cwnd = 2 * maxseg;
-		else if (maxseg > 1095)
-			tp->snd_cwnd = 3 * maxseg;
-		else
-			tp->snd_cwnd = 4 * maxseg;
-	}
+	else
+		tp->snd_cwnd = tcp_compute_initwnd(maxseg);
 
 	if (CC_ALGO(tp)->conn_init != NULL)
 		CC_ALGO(tp)->conn_init(tp->ccv);
@@ -3818,3 +3801,30 @@
 		tp->sackhint.sack_bytes_rexmit -
 		tp->sackhint.sacked_bytes);
 }
+
+uint32_t
+tcp_compute_initwnd(uint32_t maxseg)
+{
+	/*
+	 * Calculate the Initial Window, also used as Restart Window
+	 *
+	 * RFC5681 Section 3.1 specifies the default conservative values.
+	 * RFC3390 specifies slightly more aggressive values.
+	 * RFC6928 increases it to ten segments.
+	 * Support for user specified value for initial flight size.
+	 */
+	if (V_tcp_initcwnd_segments)
+		return min(V_tcp_initcwnd_segments * maxseg,
+		    max(2 * maxseg, V_tcp_initcwnd_segments * 1460));
+	else if (V_tcp_do_rfc3390)
+		return min(4 * maxseg, max(2 * maxseg, 4380));
+	else {
+		/* Per RFC5681 Section 3.1 */
+		if (maxseg > 2190)
+			return (2 * maxseg);
+		else if (maxseg > 1095)
+			return (3 * maxseg);
+		else
+			return (4 * maxseg);
+	}
+}
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -942,6 +942,7 @@
 void	 tcp_free_sackholes(struct tcpcb *tp);
 int	 tcp_newreno(struct tcpcb *, struct tcphdr *);
 int	 tcp_compute_pipe(struct tcpcb *);
+uint32_t tcp_compute_initwnd(uint32_t);
 void	 tcp_sndbuf_autoscale(struct tcpcb *, struct socket *, uint32_t);
 struct mbuf *
 	 tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,