diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
index 2eebce47075..cb709fb1e7c 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -1420,11 +1420,14 @@ tcp_mtudisc(inp, errno)
 	u_int romtu;
 	int mss;
 #ifdef INET6
-	int isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
+	int isipv6;
 #endif /* INET6 */
 	bzero(&tao, sizeof(tao));
 
 	if (tp != NULL) {
+#ifdef INET6
+		isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
+#endif
 		maxmtu = tcp_hc_getmtu(&inp->inp_inc); /* IPv4 and IPv6 */
 		romtu =
 #ifdef INET6
diff --git a/sys/netinet/tcp_timewait.c b/sys/netinet/tcp_timewait.c
index 2eebce47075..cb709fb1e7c 100644
--- a/sys/netinet/tcp_timewait.c
+++ b/sys/netinet/tcp_timewait.c
@@ -1420,11 +1420,14 @@ tcp_mtudisc(inp, errno)
 	u_int romtu;
 	int mss;
 #ifdef INET6
-	int isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
+	int isipv6;
 #endif /* INET6 */
 	bzero(&tao, sizeof(tao));
 
 	if (tp != NULL) {
+#ifdef INET6
+		isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
+#endif
 		maxmtu = tcp_hc_getmtu(&inp->inp_inc); /* IPv4 and IPv6 */
 		romtu =
 #ifdef INET6