diff --git a/sys/netinet/cc/cc.c b/sys/netinet/cc/cc.c
--- a/sys/netinet/cc/cc.c
+++ b/sys/netinet/cc/cc.c
@@ -492,7 +492,7 @@
 			if (V_tcp_do_newsack) {
 				pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 			} else {
-				pipe = CCV(ccv, snd_nxt) -
+				pipe = CCV(ccv, snd_max) -
 					CCV(ccv, snd_fack) +
 					CCV(ccv, sackhint.sack_bytes_rexmit);
 			}
diff --git a/sys/netinet/cc/cc_cubic.c b/sys/netinet/cc/cc_cubic.c
--- a/sys/netinet/cc/cc_cubic.c
+++ b/sys/netinet/cc/cc_cubic.c
@@ -479,7 +479,7 @@
 			if (V_tcp_do_newsack) {
 				pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 			} else {
-				pipe = CCV(ccv, snd_nxt) -
+				pipe = CCV(ccv, snd_max) -
 					CCV(ccv, snd_fack) +
 					CCV(ccv, sackhint.sack_bytes_rexmit);
 			}
diff --git a/sys/netinet/cc/cc_dctcp.c b/sys/netinet/cc/cc_dctcp.c
--- a/sys/netinet/cc/cc_dctcp.c
+++ b/sys/netinet/cc/cc_dctcp.c
@@ -296,7 +296,7 @@
 				if (V_tcp_do_newsack) {
 					pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 				} else {
-					pipe = CCV(ccv, snd_nxt) -
+					pipe = CCV(ccv, snd_max) -
 						CCV(ccv, snd_fack) +
 						CCV(ccv, sackhint.sack_bytes_rexmit);
 				}
diff --git a/sys/netinet/cc/cc_htcp.c b/sys/netinet/cc/cc_htcp.c
--- a/sys/netinet/cc/cc_htcp.c
+++ b/sys/netinet/cc/cc_htcp.c
@@ -327,7 +327,7 @@
 			if (V_tcp_do_newsack) {
 				pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 			} else {
-				pipe = CCV(ccv, snd_nxt) -
+				pipe = CCV(ccv, snd_max) -
 					CCV(ccv, snd_fack) +
 					CCV(ccv, sackhint.sack_bytes_rexmit);
 			}
diff --git a/sys/netinet/cc/cc_newreno.c b/sys/netinet/cc/cc_newreno.c
--- a/sys/netinet/cc/cc_newreno.c
+++ b/sys/netinet/cc/cc_newreno.c
@@ -431,7 +431,7 @@
 			if (V_tcp_do_newsack) {
 				pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 			} else {
-				pipe = CCV(ccv, snd_nxt) -
+				pipe = CCV(ccv, snd_max) -
 					CCV(ccv, snd_fack) +
 					CCV(ccv, sackhint.sack_bytes_rexmit);
 			}
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
@@ -461,6 +461,10 @@
 		tp->t_badrxtwin = 0;
 		break;
 	}
+	if (SEQ_LT(tp->snd_fack, tp->snd_una) ||
+	    SEQ_GT(tp->snd_fack, tp->snd_max)) {
+		tp->snd_fack = tp->snd_una;
+	}
 
 	if (CC_ALGO(tp)->cong_signal != NULL) {
 		if (th != NULL)