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
@@ -440,7 +440,7 @@
 	 * maximum of the former ssthresh or 3/4 of the old cwnd, to
 	 * not exit slow-start prematurely.
 	 */
-	rw = tcp_compute_initwnd(tcp_maxseg(ccv->ccvc.tcp));
+	rw = tcp_compute_initwnd(tcp_fixed_maxseg(ccv->ccvc.tcp));
 
 	CCV(ccv, snd_ssthresh) = max(CCV(ccv, snd_ssthresh),
 	    CCV(ccv, snd_cwnd)-(CCV(ccv, snd_cwnd)>>2));
@@ -454,8 +454,7 @@
 void
 newreno_cc_cong_signal(struct cc_var *ccv, uint32_t type)
 {
-	uint32_t cwin, factor;
-	u_int mss;
+	uint32_t cwin, factor, mss, pipe;
 
 	cwin = CCV(ccv, snd_cwnd);
 	mss = tcp_fixed_maxseg(ccv->ccvc.tcp);
@@ -489,9 +488,17 @@
 		}
 		break;
 	case CC_RTO:
-		CCV(ccv, snd_ssthresh) = max(min(CCV(ccv, snd_wnd),
-						 CCV(ccv, snd_cwnd)) / 2 / mss,
-					     2) * mss;
+		if (CCV(ccv, t_rxtshift) == 1) {
+			if (V_tcp_do_newsack) {
+				pipe = tcp_compute_pipe(ccv->ccvc.tcp);
+			} else {
+				pipe = CCV(ccv, snd_nxt) -
+					CCV(ccv, snd_fack) +
+					CCV(ccv, sackhint.sack_bytes_rexmit);
+			}
+			CCV(ccv, snd_ssthresh) = max(2,
+				min(CCV(ccv, snd_wnd), pipe) / 2 / mss) * mss;
+		}
 		CCV(ccv, snd_cwnd) = mss;
 		break;
 	}
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
@@ -420,10 +420,10 @@
 cubic_cong_signal(struct cc_var *ccv, uint32_t type)
 {
 	struct cubic *cubic_data;
-	u_int mss;
+	uint32_t mss, pipe;
 
 	cubic_data = ccv->cc_data;
-	mss = tcp_maxseg(ccv->ccvc.tcp);
+	mss = tcp_fixed_maxseg(ccv->ccvc.tcp);
 
 	switch (type) {
 	case CC_NDUPACK:
@@ -476,12 +476,20 @@
 			cubic_data->undo_cwnd_prior = cubic_data->cwnd_prior;
 			cubic_data->undo_W_max = cubic_data->W_max;
 			cubic_data->undo_K = cubic_data->K;
+			if (V_tcp_do_newsack) {
+				pipe = tcp_compute_pipe(ccv->ccvc.tcp);
+			} else {
+				pipe = CCV(ccv, snd_nxt) -
+					CCV(ccv, snd_fack) +
+					CCV(ccv, sackhint.sack_bytes_rexmit);
+			}
+			CCV(ccv, snd_ssthresh) = max(2,
+				(((uint64_t)min(CCV(ccv, snd_wnd), pipe) *
+				CUBIC_BETA) >> CUBIC_SHIFT) / mss) * mss;
 		}
 		cubic_data->flags |= CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT;
 		cubic_data->undo_W_max = cubic_data->W_max;
 		cubic_data->num_cong_events++;
-			CCV(ccv, snd_ssthresh) = ((uint64_t)CCV(ccv, snd_cwnd) *
-					  CUBIC_BETA) >> CUBIC_SHIFT;
 		CCV(ccv, snd_cwnd) = mss;
 		break;
 
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
@@ -240,12 +240,12 @@
 dctcp_cong_signal(struct cc_var *ccv, uint32_t type)
 {
 	struct dctcp *dctcp_data;
-	u_int cwin, mss;
+	uint32_t cwin, mss, pipe;
 
 	if (CCV(ccv, t_flags2) & TF2_ECN_PERMIT) {
 		dctcp_data = ccv->cc_data;
 		cwin = CCV(ccv, snd_cwnd);
-		mss = tcp_maxseg(ccv->ccvc.tcp);
+		mss = tcp_fixed_maxseg(ccv->ccvc.tcp);
 
 		switch (type) {
 		case CC_NDUPACK:
@@ -292,9 +292,17 @@
 			dctcp_data->ece_curr = 1;
 			break;
 		case CC_RTO:
-			CCV(ccv, snd_ssthresh) = max(min(CCV(ccv, snd_wnd),
-							 CCV(ccv, snd_cwnd)) / 2 / mss,
-						     2) * mss;
+			if (CCV(ccv, t_rxtshift) == 1) {
+				if (V_tcp_do_newsack) {
+					pipe = tcp_compute_pipe(ccv->ccvc.tcp);
+				} else {
+					pipe = CCV(ccv, snd_nxt) -
+						CCV(ccv, snd_fack) +
+						CCV(ccv, sackhint.sack_bytes_rexmit);
+				}
+				CCV(ccv, snd_ssthresh) = max(2,
+					min(CCV(ccv, snd_wnd), pipe) / 2 / mss) * mss;
+			}
 			CCV(ccv, snd_cwnd) = mss;
 			dctcp_update_alpha(ccv);
 			dctcp_data->save_sndnxt += CCV(ccv, t_maxseg);
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
@@ -281,10 +281,10 @@
 htcp_cong_signal(struct cc_var *ccv, uint32_t type)
 {
 	struct htcp *htcp_data;
-	u_int mss;
+	uint32_t mss, pipe;
 
 	htcp_data = ccv->cc_data;
-	mss = tcp_maxseg(ccv->ccvc.tcp);
+	mss = tcp_fixed_maxseg(ccv->ccvc.tcp);
 
 	switch (type) {
 	case CC_NDUPACK:
@@ -323,9 +323,17 @@
 		break;
 
 	case CC_RTO:
-		CCV(ccv, snd_ssthresh) = max(min(CCV(ccv, snd_wnd),
-						 CCV(ccv, snd_cwnd)) / 2 / mss,
-					     2) * mss;
+		if (CCV(ccv, t_rxtshift) == 1) {
+			if (V_tcp_do_newsack) {
+				pipe = tcp_compute_pipe(ccv->ccvc.tcp);
+			} else {
+				pipe = CCV(ccv, snd_nxt) -
+					CCV(ccv, snd_fack) +
+					CCV(ccv, sackhint.sack_bytes_rexmit);
+			}
+			CCV(ccv, snd_ssthresh) = max(2,
+				min(CCV(ccv, snd_wnd), pipe) / 2 / mss) * mss;
+		}
 		CCV(ccv, snd_cwnd) = mss;
 		/*
 		 * Grab the current time and record it so we know when the
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
@@ -366,8 +366,7 @@
 newreno_cong_signal(struct cc_var *ccv, uint32_t type)
 {
 	struct newreno *nreno;
-	uint32_t beta, beta_ecn, cwin, factor;
-	u_int mss;
+	uint32_t beta, beta_ecn, cwin, factor, mss, pipe;
 
 	cwin = CCV(ccv, snd_cwnd);
 	mss = tcp_fixed_maxseg(ccv->ccvc.tcp);
@@ -428,9 +427,19 @@
 		}
 		break;
 	case CC_RTO:
-		CCV(ccv, snd_ssthresh) = max(min(CCV(ccv, snd_wnd),
-						 CCV(ccv, snd_cwnd)) / 2 / mss,
-					     2) * mss;
+		if (CCV(ccv, t_rxtshift) == 1) {
+			if (V_tcp_do_newsack) {
+				pipe = tcp_compute_pipe(ccv->ccvc.tcp);
+			} else {
+				pipe = CCV(ccv, snd_nxt) -
+					CCV(ccv, snd_fack) +
+					CCV(ccv, sackhint.sack_bytes_rexmit);
+			}
+			CCV(ccv, snd_ssthresh) = max(2,
+				((uint64_t)min(CCV(ccv, snd_wnd), pipe) *
+				    (uint64_t)factor) /
+				    (100ULL * (uint64_t)mss)) * mss;
+		}
 		CCV(ccv, snd_cwnd) = mss;
 		break;
 	}
diff --git a/sys/netinet/tcp_stacks/rack.c b/sys/netinet/tcp_stacks/rack.c
--- a/sys/netinet/tcp_stacks/rack.c
+++ b/sys/netinet/tcp_stacks/rack.c
@@ -5948,8 +5948,11 @@
 		tp->t_bytes_acked = 0;
 		rack->r_fast_output = 0;
 		EXIT_RECOVERY(tp->t_flags);
-		tp->snd_ssthresh = max(2, min(tp->snd_wnd, rack->r_ctl.cwnd_to_use) / 2 /
-		    ctf_fixed_maxseg(tp)) * ctf_fixed_maxseg(tp);
+		if (tp->t_rxtshift == 1) {
+			tp->snd_ssthresh = max(2,
+			    min(tp->snd_wnd, rack->r_ctl.cwnd_to_use) / 2 /
+			    ctf_fixed_maxseg(tp)) * ctf_fixed_maxseg(tp);
+		}
 		orig_cwnd = tp->snd_cwnd;
 		tp->snd_cwnd = ctf_fixed_maxseg(tp);
 		rack_log_to_prr(rack, 16, orig_cwnd, line);