Index: head/sys/netinet/tcp_output.c
===================================================================
--- head/sys/netinet/tcp_output.c
+++ head/sys/netinet/tcp_output.c
@@ -656,7 +656,8 @@
 		if (adv >= (int32_t)(2 * tp->t_maxseg) &&
 		    (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
 		     recwin <= (so->so_rcv.sb_hiwat / 8) ||
-		     so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
+		     so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg ||
+		     adv >= TCP_MAXWIN << tp->rcv_scale))
 			goto send;
 		if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
 			goto send;