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
@@ -392,6 +392,7 @@
 newreno_cc_post_recovery(struct cc_var *ccv)
 {
 	int pipe;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	if (IN_FASTRECOVERY(CCV(ccv, t_flags))) {
 		/*
@@ -412,8 +413,7 @@
 			 * Ensure that cwnd does not collapse to 1 MSS under
 			 * adverse conditions. Implements RFC6582
 			 */
-			CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) +
-			    CCV(ccv, t_maxseg);
+			CCV(ccv, snd_cwnd) = max(pipe, mss) + mss;
 		else
 			CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
 	}
@@ -521,7 +521,7 @@
 newreno_cc_cwnd_in_cong_avoid(struct cc_var *ccv)
 {
 	u_int cw = CCV(ccv, snd_cwnd);
-	u_int incr = CCV(ccv, t_maxseg);
+	u_int incr = tcp_fixed_maxseg(ccv->tp);
 
 	KASSERT(cw > CCV(ccv, snd_ssthresh),
 		("congestion control state not in congestion avoidance\n"));
@@ -561,7 +561,8 @@
 newreno_cc_cwnd_in_slow_start(struct cc_var *ccv)
 {
 	u_int cw = CCV(ccv, snd_cwnd);
-	u_int incr = CCV(ccv, t_maxseg);
+	u_int mss = tcp_fixed_maxseg(ccv->tp);
+	u_int incr = mss;
 
 	KASSERT(cw <= CCV(ccv, snd_ssthresh),
 		("congestion control state not in slow start\n"));
@@ -599,9 +600,9 @@
 			abc_val = V_tcp_abc_l_var;
 		if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max))
 			incr = min(ccv->bytes_this_ack,
-			           ccv->nsegs * abc_val * CCV(ccv, t_maxseg));
+			           ccv->nsegs * abc_val * mss);
 		else
-			incr = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg));
+			incr = min(ccv->bytes_this_ack, mss);
 	}
 	/* ABC is on by default, so incr equals 0 frequently. */
 	if (incr > 0)
diff --git a/sys/netinet/cc/cc_cdg.c b/sys/netinet/cc/cc_cdg.c
--- a/sys/netinet/cc/cc_cdg.c
+++ b/sys/netinet/cc/cc_cdg.c
@@ -416,27 +416,28 @@
 {
 	struct cdg *cdg_data;
 	int incr, s_w_incr;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	cdg_data = ccv->cc_data;
 	incr = s_w_incr = 0;
 
 	if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh)) {
 		/* Slow start. */
-		incr = CCV(ccv, t_maxseg);
+		incr = mss;
 		s_w_incr = incr;
 		cdg_data->window_incr = cdg_data->rtt_count = 0;
 	} else {
 		/* Congestion avoidance. */
 		if (new_measurement) {
-			s_w_incr = CCV(ccv, t_maxseg);
+			s_w_incr = mss;
 			if (V_cdg_alpha_inc == 0) {
-				incr = CCV(ccv, t_maxseg);
+				incr = mss;
 			} else {
 				if (++cdg_data->rtt_count >= V_cdg_alpha_inc) {
 					cdg_data->window_incr++;
 					cdg_data->rtt_count = 0;
 				}
-				incr = CCV(ccv, t_maxseg) *
+				incr = mss *
 				    cdg_data->window_incr;
 			}
 		}
diff --git a/sys/netinet/cc/cc_chd.c b/sys/netinet/cc/cc_chd.c
--- a/sys/netinet/cc/cc_chd.c
+++ b/sys/netinet/cc/cc_chd.c
@@ -147,10 +147,11 @@
 chd_window_decrease(struct cc_var *ccv)
 {
 	unsigned long win;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
-	win = min(CCV(ccv, snd_wnd), CCV(ccv, snd_cwnd)) / CCV(ccv, t_maxseg);
+	win = min(CCV(ccv, snd_wnd), CCV(ccv, snd_cwnd)) / mss;
 	win -= max((win / 2), 1);
-	CCV(ccv, snd_ssthresh) = max(win, 2) * CCV(ccv, t_maxseg);
+	CCV(ccv, snd_ssthresh) = max(win, 2) * mss;
 }
 
 /*
@@ -190,6 +191,7 @@
 {
 	struct chd *chd_data;
 	int incr;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	chd_data = ccv->cc_data;
 	incr = 0;
@@ -201,23 +203,22 @@
 			if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max)) {
 				/* Not due to RTO. */
 				incr = min(ccv->bytes_this_ack,
-				    V_tcp_abc_l_var * CCV(ccv, t_maxseg));
+				    V_tcp_abc_l_var * mss);
 			} else {
 				/* Due to RTO. */
-				incr = min(ccv->bytes_this_ack,
-				    CCV(ccv, t_maxseg));
+				incr = min(ccv->bytes_this_ack, mss);
 			}
 		} else
-			incr = CCV(ccv, t_maxseg);
+			incr = mss;
 
 	} else { /* Congestion avoidance. */
 		if (V_tcp_do_rfc3465) {
 			if (ccv->flags & CCF_ABC_SENTAWND) {
 				ccv->flags &= ~CCF_ABC_SENTAWND;
-				incr = CCV(ccv, t_maxseg);
+				incr = mss;
 			}
 		} else if (new_measurement)
-			incr = CCV(ccv, t_maxseg);
+			incr = mss;
 	}
 
 	if (chd_data->shadow_w > 0) {
@@ -380,8 +381,9 @@
 		}
 
 		if (chd_data->shadow_w > 0) {
+			uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 			chd_data->shadow_w = max(chd_data->shadow_w /
-			    CCV(ccv, t_maxseg) / 2, 2) * CCV(ccv, t_maxseg);
+			    mss / 2, 2) * mss;
 		}
 		ENTER_FASTRECOVERY(CCV(ccv, t_flags));
 		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
@@ -168,7 +168,8 @@
 	 * doesn't rely on tcpcb vars.
 	 */
 	u_int cw = CCV(ccv, snd_cwnd);
-	u_int incr = CCV(ccv, t_maxseg);
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
+	u_int incr = mss;
 	uint16_t abc_val;
 
 	cubicd->flags |= CUBICFLAG_IN_SLOWSTART;
@@ -216,10 +217,9 @@
 	}
 	if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max))
 		incr = min(ccv->bytes_this_ack,
-			   ccv->nsegs * abc_val *
-			   CCV(ccv, t_maxseg));
+			   ccv->nsegs * abc_val * mss);
 	else
-		incr = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg));
+		incr = min(ccv->bytes_this_ack, mss);
 
 	/* Only if Hystart is enabled will the flag get set */
 	if (cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) {
@@ -238,6 +238,7 @@
 	struct cubic *cubic_data;
 	unsigned long W_est, W_cubic;
 	int usecs_since_epoch;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	cubic_data = ccv->cc_data;
 	cubic_record_rtt(ccv);
@@ -277,8 +278,7 @@
 				cubic_data->flags &= ~(CUBICFLAG_IN_SLOWSTART |
 						       CUBICFLAG_IN_APPLIMIT);
 				cubic_data->t_epoch = ticks;
-				cubic_data->K = cubic_k(cubic_data->W_max /
-							CCV(ccv, t_maxseg));
+				cubic_data->K = cubic_k(cubic_data->W_max / mss);
 			}
 			usecs_since_epoch = (ticks - cubic_data->t_epoch) * tick;
 			if (usecs_since_epoch < 0) {
@@ -298,7 +298,7 @@
 			W_cubic = cubic_cwnd(usecs_since_epoch +
 					     cubic_data->mean_rtt_usecs,
 					     cubic_data->W_max,
-					     CCV(ccv, t_maxseg),
+					     tcp_fixed_maxseg(ccv->tp),
 					     cubic_data->K);
 
 			if (W_cubic < W_est) {
@@ -329,7 +329,7 @@
 			    cubic_data->W_max < CCV(ccv, snd_cwnd)) {
 				cubic_data->W_max = CCV(ccv, snd_cwnd);
 				cubic_data->K = cubic_k(cubic_data->W_max /
-				    CCV(ccv, t_maxseg));
+				    tcp_fixed_maxseg(ccv->tp));
 			}
 		}
 	} else if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
@@ -351,7 +351,7 @@
 	cubic_data = ccv->cc_data;
 
 	cubic_data->W_max = ulmax(cubic_data->W_max, CCV(ccv, snd_cwnd));
-	cubic_data->K = cubic_k(cubic_data->W_max / CCV(ccv, t_maxseg));
+	cubic_data->K = cubic_k(cubic_data->W_max / tcp_fixed_maxseg(ccv->tp));
 	if ((cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) == 0) {
 		/*
 		 * Re-enable hystart if we have been idle.
@@ -532,6 +532,7 @@
 {
 	struct cubic *cubic_data;
 	int pipe;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	cubic_data = ccv->cc_data;
 	pipe = 0;
@@ -554,13 +555,12 @@
 			 * Ensure that cwnd does not collapse to 1 MSS under
 			 * adverse conditions. Implements RFC6582
 			 */
-			CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) +
-			    CCV(ccv, t_maxseg);
+			CCV(ccv, snd_cwnd) = max(pipe, mss) + mss;
 		else
 			/* Update cwnd based on beta and adjusted W_max. */
 			CCV(ccv, snd_cwnd) = max(((uint64_t)cubic_data->W_max *
 			    CUBIC_BETA) >> CUBIC_SHIFT,
-			    2 * CCV(ccv, t_maxseg));
+			    2 * mss);
 	}
 
 	/* Calculate the average RTT between congestion epochs. */
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
@@ -108,6 +108,7 @@
 {
 	struct dctcp *dctcp_data;
 	int bytes_acked = 0;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	dctcp_data = ccv->cc_data;
 
@@ -125,7 +126,7 @@
 			newreno_cc_ack_received(ccv, type);
 
 		if (type == CC_DUPACK)
-			bytes_acked = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg));
+			bytes_acked = min(ccv->bytes_this_ack, mss);
 
 		if (type == CC_ACK)
 			bytes_acked = ccv->bytes_this_ack;
@@ -138,16 +139,16 @@
 			//XXRMS: For fluid-model DCTCP, update
 			//cwnd here during for RTT fairness
 			if (!dctcp_data->ece_prev
-			    && bytes_acked > CCV(ccv, t_maxseg)) {
+			    && bytes_acked > mss) {
 				dctcp_data->bytes_ecn +=
-				    (bytes_acked - CCV(ccv, t_maxseg));
+				    (bytes_acked - mss);
 			} else
 				dctcp_data->bytes_ecn += bytes_acked;
 			dctcp_data->ece_prev = 1;
 		} else {
 			if (dctcp_data->ece_prev
-			    && bytes_acked > CCV(ccv, t_maxseg))
-				dctcp_data->bytes_ecn += CCV(ccv, t_maxseg);
+			    && bytes_acked > mss)
+				dctcp_data->bytes_ecn += mss;
 			dctcp_data->ece_prev = 0;
 		}
 		dctcp_data->ece_curr = 0;
@@ -305,7 +306,7 @@
 			}
 			CCV(ccv, snd_cwnd) = mss;
 			dctcp_update_alpha(ccv);
-			dctcp_data->save_sndnxt += CCV(ccv, t_maxseg);
+			dctcp_data->save_sndnxt += mss;
 			dctcp_data->num_cong_events++;
 			break;
 		default:
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
@@ -193,6 +193,7 @@
 htcp_ack_received(struct cc_var *ccv, ccsignal_t type)
 {
 	struct htcp *htcp_data;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	htcp_data = ccv->cc_data;
 	htcp_record_rtt(ccv);
@@ -220,7 +221,7 @@
 			if (V_tcp_do_rfc3465) {
 				/* Increment cwnd by alpha segments. */
 				CCV(ccv, snd_cwnd) += htcp_data->alpha *
-				    CCV(ccv, t_maxseg);
+				    mss;
 				ccv->flags &= ~CCF_ABC_SENTAWND;
 			} else
 				/*
@@ -230,8 +231,8 @@
 				 */
 				CCV(ccv, snd_cwnd) += (((htcp_data->alpha <<
 				    HTCP_SHIFT) / (max(1,
-				    CCV(ccv, snd_cwnd) / CCV(ccv, t_maxseg)))) *
-				    CCV(ccv, t_maxseg))  >> HTCP_SHIFT;
+				    CCV(ccv, snd_cwnd) / mss))) *
+				    mss)  >> HTCP_SHIFT;
 		}
 	}
 }
@@ -370,6 +371,7 @@
 {
 	int pipe;
 	struct htcp *htcp_data;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	pipe = 0;
 	htcp_data = ccv->cc_data;
@@ -392,12 +394,11 @@
 			 * Ensure that cwnd down not collape to 1 MSS under
 			 * adverse conditions. Implements RFC6582
 			 */
-			CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) +
-			    CCV(ccv, t_maxseg);
+			CCV(ccv, snd_cwnd) = max(pipe, mss) + mss;
 		else
 			CCV(ccv, snd_cwnd) = max(1, ((htcp_data->beta *
-			    htcp_data->prev_cwnd / CCV(ccv, t_maxseg))
-			    >> HTCP_SHIFT)) * CCV(ccv, t_maxseg);
+			    htcp_data->prev_cwnd / mss)
+			    >> HTCP_SHIFT)) * mss;
 	}
 }
 
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
@@ -215,12 +215,13 @@
 newreno_ack_received(struct cc_var *ccv, ccsignal_t type)
 {
 	struct newreno *nreno;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	nreno = ccv->cc_data;
 	if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
 	    (ccv->flags & CCF_CWND_LIMITED)) {
 		u_int cw = CCV(ccv, snd_cwnd);
-		u_int incr = CCV(ccv, t_maxseg);
+		u_int incr = mss;
 
 		/*
 		 * Regular in-order ACK, open the congestion window.
@@ -324,10 +325,9 @@
 			}
 			if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max))
 				incr = min(ccv->bytes_this_ack,
-				    ccv->nsegs * abc_val *
-				    CCV(ccv, t_maxseg));
+				    ccv->nsegs * abc_val * mss);
 			else
-				incr = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg));
+				incr = min(ccv->bytes_this_ack, mss);
 
 			/* Only if Hystart is enabled will the flag get set */
 			if (nreno->newreno_flags & CC_NEWRENO_HYSTART_IN_CSS) {
diff --git a/sys/netinet/cc/cc_vegas.c b/sys/netinet/cc/cc_vegas.c
--- a/sys/netinet/cc/cc_vegas.c
+++ b/sys/netinet/cc/cc_vegas.c
@@ -129,6 +129,7 @@
 	struct ertt *e_t;
 	struct vegas *vegas_data;
 	long actual_tx_rate, expected_tx_rate, ndiff;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	e_t = khelp_get_osd(&CCV(ccv, t_osd), ertt_id);
 	vegas_data = ccv->cc_data;
@@ -139,7 +140,7 @@
 			actual_tx_rate = e_t->bytes_tx_in_marked_rtt /
 			    e_t->markedpkt_rtt;
 			ndiff = (expected_tx_rate - actual_tx_rate) *
-			    e_t->minrtt / CCV(ccv, t_maxseg);
+			    e_t->minrtt / mss;
 
 			if (ndiff < V_vegas_alpha) {
 				if (CCV(ccv, snd_cwnd) <=
@@ -150,8 +151,7 @@
 				} else {
 					vegas_data->slow_start_toggle = 0;
 					CCV(ccv, snd_cwnd) =
-					    min(CCV(ccv, snd_cwnd) +
-					    CCV(ccv, t_maxseg),
+					    min(CCV(ccv, snd_cwnd) + mss,
 					    TCP_MAXWIN << CCV(ccv, snd_scale));
 				}
 			} else if (ndiff > V_vegas_beta) {
@@ -207,6 +207,7 @@
 {
 	struct vegas *vegas_data;
 	int presignalrecov;
+	uint32_t mss = tcp_fixed_maxseg(ccv->tp);
 
 	vegas_data = ccv->cc_data;
 
@@ -218,8 +219,8 @@
 	switch((int)signal_type) {
 	case CC_VEGAS_RATE:
 		if (!IN_RECOVERY(CCV(ccv, t_flags))) {
-			CCV(ccv, snd_cwnd) = max(2 * CCV(ccv, t_maxseg),
-			    CCV(ccv, snd_cwnd) - CCV(ccv, t_maxseg));
+			CCV(ccv, snd_cwnd) = max(2 * mss,
+			    CCV(ccv, snd_cwnd) - mss);
 			if (CCV(ccv, snd_cwnd) < CCV(ccv, snd_ssthresh))
 				/* Exit slow start. */
 				CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd);
diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -1695,7 +1695,7 @@
 			return (error);
 		case ENOBUFS:
 			TCP_XMIT_TIMER_ASSERT(tp, len, flags);
-			tp->snd_cwnd = tp->t_maxseg;
+			tp->snd_cwnd = tcp_maxseg(tp);
 			return (0);
 		case EMSGSIZE:
 			/*