Index: tcp_input.c
===================================================================
--- tcp_input.c	(revision 228200)
+++ tcp_input.c	(working copy)
@@ -1795,9 +1795,6 @@
 	win = sbspace(&so->so_rcv);
 	if (win < 0)
 		win = 0;
-	KASSERT(SEQ_GEQ(tp->rcv_adv, tp->rcv_nxt),
-	    ("tcp_input negative window: tp %p rcv_nxt %u rcv_adv %u", tp,
-	    tp->rcv_nxt, tp->rcv_adv));
 	tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
 
 	/* Reset receive buffer auto scaling when not in bulk receive mode. */
Index: tcp_timewait.c
===================================================================
--- tcp_timewait.c	(revision 228200)
+++ tcp_timewait.c	(working copy)
@@ -242,10 +242,10 @@
 	/*
 	 * Recover last window size sent.
 	 */
-	KASSERT(SEQ_GEQ(tp->rcv_adv, tp->rcv_nxt),
-	    ("tcp_twstart negative window: tp %p rcv_nxt %u rcv_adv %u", tp,
-	    tp->rcv_nxt, tp->rcv_adv));
-	tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale;
+	if (SEQ_GE(tp->rcv_adv, tp->rcv_nxt))
+		tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale;
+	else
+		tw->last_win = 0;
 
 	/*
 	 * Set t_recent if timestamps are used on the connection.