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));
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
@@ -423,7 +423,7 @@
 	u_int mss;
 
 	cubic_data = ccv->cc_data;
-	mss = tcp_maxseg(ccv->ccvc.tcp);
+	mss = tcp_fixed_maxseg(ccv->ccvc.tcp);
 
 	switch (type) {
 	case CC_NDUPACK:
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
@@ -245,7 +245,7 @@
 	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:
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
@@ -284,7 +284,7 @@
 	u_int mss;
 
 	htcp_data = ccv->cc_data;
-	mss = tcp_maxseg(ccv->ccvc.tcp);
+	mss = tcp_fixed_maxseg(ccv->ccvc.tcp);
 
 	switch (type) {
 	case CC_NDUPACK: