diff --git a/sys/netinet/tcp_usrreq.c b/sys/netinet/tcp_usrreq.c
--- a/sys/netinet/tcp_usrreq.c
+++ b/sys/netinet/tcp_usrreq.c
@@ -2482,7 +2482,7 @@
 			error = sooptcopyout(sopt, &optval, sizeof optval);
 			break;
 		case TCP_MAXSEG:
-			optval = tp->t_maxseg;
+			optval = tcp_maxseg(tp);
 			INP_WUNLOCK(inp);
 			error = sooptcopyout(sopt, &optval, sizeof optval);
 			break;