Index: head/sys/netinet/tcp_output.c
===================================================================
--- head/sys/netinet/tcp_output.c
+++ head/sys/netinet/tcp_output.c
@@ -1238,8 +1238,11 @@
 	if (flags & TH_SYN)
 		th->th_win = htons((u_short)
 				(min(sbspace(&so->so_rcv), TCP_MAXWIN)));
-	else
+	else {
+		/* Avoid shrinking window with window scaling. */
+		recwin = roundup2(recwin, 1 << tp->rcv_scale);
 		th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
+	}
 
 	/*
 	 * Adjust the RXWIN0SENT flag - indicate that we have advertised
Index: head/sys/netinet/tcp_stacks/bbr.c
===================================================================
--- head/sys/netinet/tcp_stacks/bbr.c
+++ head/sys/netinet/tcp_stacks/bbr.c
@@ -13756,8 +13756,11 @@
 	if (flags & TH_SYN)
 		th->th_win = htons((u_short)
 		    (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
-	else
+	else {
+		/* Avoid shrinking window with window scaling. */
+		recwin = roundup2(recwin, 1 << tp->rcv_scale);
 		th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
+	}
 	/*
 	 * Adjust the RXWIN0SENT flag - indicate that we have advertised a 0
 	 * window.  This may cause the remote transmitter to stall.  This
Index: head/sys/netinet/tcp_stacks/rack.c
===================================================================
--- head/sys/netinet/tcp_stacks/rack.c
+++ head/sys/netinet/tcp_stacks/rack.c
@@ -9572,8 +9572,11 @@
 	if (flags & TH_SYN)
 		th->th_win = htons((u_short)
 		    (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
-	else
+	else {
+		/* Avoid shrinking window with window scaling. */
+		recwin = roundup2(recwin, 1 << tp->rcv_scale);
 		th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
+	}
 	/*
 	 * Adjust the RXWIN0SENT flag - indicate that we have advertised a 0
 	 * window.  This may cause the remote transmitter to stall.  This