Index: head/sys/netinet/cc/cc_cdg.c
===================================================================
--- head/sys/netinet/cc/cc_cdg.c
+++ head/sys/netinet/cc/cc_cdg.c
@@ -474,7 +474,9 @@
 		ENTER_RECOVERY(CCV(ccv, t_flags));
 		break;
 	case CC_RTO:
-		CCV(ccv, snd_ssthresh) = max(2*mss, cwin/2);
+		CCV(ccv, snd_ssthresh) =
+		    max((CCV(ccv, snd_max) - CCV(ccv, snd_una)) / 2 / mss, 2)
+			* mss;
 		CCV(ccv, snd_cwnd) = mss;
 		break;
 	default:
Index: head/sys/netinet/cc/cc_chd.c
===================================================================
--- head/sys/netinet/cc/cc_chd.c
+++ head/sys/netinet/cc/cc_chd.c
@@ -330,13 +330,11 @@
 	struct ertt *e_t;
 	struct chd *chd_data;
 	int qdly;
-	uint32_t cwin;
 	u_int mss;
 
 	e_t = khelp_get_osd(CCV(ccv, osd), ertt_id);
 	chd_data = ccv->cc_data;
 	qdly = imax(e_t->rtt, chd_data->maxrtt_in_rtt) - e_t->minrtt;
-	cwin = CCV(ccv, snd_cwnd);
 	mss = CCV(ccv, t_maxseg);
 
 	switch(signal_type) {
@@ -378,7 +376,9 @@
 		ENTER_FASTRECOVERY(CCV(ccv, t_flags));
 		break;
 	case CC_RTO:
-		CCV(ccv, snd_ssthresh) = max(2*mss, cwin/2);
+		CCV(ccv, snd_ssthresh) =
+		    max((CCV(ccv, snd_max) - CCV(ccv, snd_una)) / 2 / mss, 2)
+			* mss;
 		CCV(ccv, snd_cwnd) = mss;
 		break;
 
Index: head/sys/netinet/cc/cc_dctcp.c
===================================================================
--- head/sys/netinet/cc/cc_dctcp.c
+++ head/sys/netinet/cc/cc_dctcp.c
@@ -230,19 +230,21 @@
 dctcp_cong_signal(struct cc_var *ccv, uint32_t type)
 {
 	struct dctcp *dctcp_data;
-	uint32_t cwin;
+	uint32_t cwin, ssthresh_on_loss;
 	u_int mss;
 
 	dctcp_data = ccv->cc_data;
 	cwin = CCV(ccv, snd_cwnd);
 	mss = CCV(ccv, t_maxseg);
+	ssthresh_on_loss =
+	    max((CCV(ccv, snd_max) - CCV(ccv, snd_una)) / 2 / mss, 2)
+		* mss;
 
 	switch (type) {
 	case CC_NDUPACK:
 		if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
 			if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
-				CCV(ccv, snd_ssthresh) = mss *
-				    max(cwin / 2 / mss, 2);
+				CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
 				dctcp_data->num_cong_events++;
 			} else {
 				/* cwnd has already updated as congestion
@@ -250,8 +252,7 @@
 				 * snd_cwnd_prev and recalculate snd_ssthresh
 				 */
 				cwin = CCV(ccv, snd_cwnd_prev);
-				CCV(ccv, snd_ssthresh) =
-				    max(cwin / 2 / mss, 2) * mss;
+				CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
 			}
 			ENTER_RECOVERY(CCV(ccv, t_flags));
 		}
@@ -265,8 +266,7 @@
 		if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
 			if (V_dctcp_slowstart &&
 			    dctcp_data->num_cong_events++ == 0) {
-				CCV(ccv, snd_ssthresh) =
-				    mss * max(cwin / 2 / mss, 2);
+				CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
 				dctcp_data->alpha = MAX_ALPHA_VALUE;
 				dctcp_data->bytes_ecn = 0;
 				dctcp_data->bytes_total = 0;
@@ -285,7 +285,7 @@
 			dctcp_update_alpha(ccv);
 			dctcp_data->save_sndnxt += CCV(ccv, t_maxseg);
 			dctcp_data->num_cong_events++;
-			CCV(ccv, snd_ssthresh) = max(2 * mss, cwin / 2);
+			CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
 			CCV(ccv, snd_cwnd) = mss;
 		}
 		break;
Index: head/sys/netinet/cc/cc_htcp.c
===================================================================
--- head/sys/netinet/cc/cc_htcp.c
+++ head/sys/netinet/cc/cc_htcp.c
@@ -325,7 +325,9 @@
 		 */
 		if (CCV(ccv, t_rxtshift) >= 2)
 			htcp_data->t_last_cong = ticks;
-		CCV(ccv, snd_ssthresh) = max(2 * mss, cwin / 2);
+		CCV(ccv, snd_ssthresh) =
+		    max((CCV(ccv, snd_max) - CCV(ccv, snd_una)) / 2 / mss, 2)
+			* mss;
 		CCV(ccv, snd_cwnd) = mss;
 		break;
 	}
@@ -518,6 +520,10 @@
 		CCV(ccv, snd_ssthresh) = ((u_long)CCV(ccv, snd_cwnd) *
 		    htcp_data->beta) >> HTCP_SHIFT;
 	}
+
+	/* Align ssthresh to MSS boundary */
+	CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_ssthresh) / CCV(ccv, t_maxseg))
+	    * CCV(ccv, t_maxseg);
 }
 
 
Index: head/sys/netinet/cc/cc_newreno.c
===================================================================
--- head/sys/netinet/cc/cc_newreno.c
+++ head/sys/netinet/cc/cc_newreno.c
@@ -182,23 +182,26 @@
 static void
 newreno_cong_signal(struct cc_var *ccv, uint32_t type)
 {
-	uint32_t cwin;
+	uint32_t cwin, ssthresh_on_loss;
 	u_int mss;
 
 	cwin = CCV(ccv, snd_cwnd);
 	mss = CCV(ccv, t_maxseg);
+	ssthresh_on_loss =
+	    max((CCV(ccv, snd_max) - CCV(ccv, snd_una)) / 2 / mss, 2)
+		* mss;
 
 	/* Catch algos which mistakenly leak private signal types. */
 	KASSERT((type & CC_SIGPRIVMASK) == 0,
 	    ("%s: congestion signal type 0x%08x is private\n", __func__, type));
 
-	cwin = max(2*mss, cwin/2);
+	cwin = max(cwin / 2 / mss, 2) * mss;
 
 	switch (type) {
 	case CC_NDUPACK:
 		if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
 			if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
-				CCV(ccv, snd_ssthresh) = cwin;
+				CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
 				CCV(ccv, snd_cwnd) = cwin;
 			}
 			ENTER_RECOVERY(CCV(ccv, t_flags));
@@ -206,13 +209,13 @@
 		break;
 	case CC_ECN:
 		if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
-			CCV(ccv, snd_ssthresh) = cwin;
+			CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
 			CCV(ccv, snd_cwnd) = cwin;
 			ENTER_CONGRECOVERY(CCV(ccv, t_flags));
 		}
 		break;
 	case CC_RTO:
-		CCV(ccv, snd_ssthresh) = cwin;
+		CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
 		CCV(ccv, snd_cwnd) = mss;
 		break;
 	}
Index: head/sys/netinet/tcp_input.c
===================================================================
--- head/sys/netinet/tcp_input.c
+++ head/sys/netinet/tcp_input.c
@@ -444,7 +444,8 @@
 			 * ssthresh = max (FlightSize / 2, 2*SMSS) eq (4)
 			 */
 			tp->snd_ssthresh =
-			    max((tp->snd_max - tp->snd_una) / 2, 2 * maxseg);
+			    max((tp->snd_max - tp->snd_una) / 2 / maxseg, 2)
+				* maxseg;
 			tp->snd_cwnd = maxseg;
 		}
 		break;