Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -3560,7 +3560,7 @@
     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
 {
 	int mss = 0;
-	u_long maxmtu = 0;
+	uint32_t maxmtu = 0;
 	struct inpcb *inp = tp->t_inpcb;
 	struct hc_metrics_lite metrics;
 #ifdef INET6
@@ -3776,7 +3776,7 @@
 {
 	int mss = 0;
 	uint32_t thcmtu = 0;
-	u_long maxmtu = 0;
+	uint32_t maxmtu = 0;
 	size_t min_protoh;
 
 	KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
Index: sys/netinet/tcp_subr.c
===================================================================
--- sys/netinet/tcp_subr.c
+++ sys/netinet/tcp_subr.c
@@ -2299,12 +2299,12 @@
  * is called by TCP routines that access the rmx structure and by
  * tcp_mss_update to get the peer/interface MTU.
  */
-u_long
+uint32_t
 tcp_maxmtu(struct in_conninfo *inc, struct tcp_ifcap *cap)
 {
 	struct nhop4_extended nh4;
 	struct ifnet *ifp;
-	u_long maxmtu = 0;
+	uint32_t maxmtu = 0;
 
 	KASSERT(inc != NULL, ("tcp_maxmtu with NULL in_conninfo pointer"));
 
@@ -2334,14 +2334,14 @@
 #endif /* INET */
 
 #ifdef INET6
-u_long
+uint32_t
 tcp_maxmtu6(struct in_conninfo *inc, struct tcp_ifcap *cap)
 {
 	struct nhop6_extended nh6;
 	struct in6_addr dst6;
 	uint32_t scopeid;
 	struct ifnet *ifp;
-	u_long maxmtu = 0;
+	uint32_t maxmtu = 0;
 
 	KASSERT(inc != NULL, ("tcp_maxmtu6 with NULL in_conninfo pointer"));
 
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -789,8 +789,8 @@
 struct tcp_function_block *find_and_ref_tcp_fb(struct tcp_function_block *blk);
 int tcp_default_ctloutput(struct socket *so, struct sockopt *sopt, struct inpcb *inp, struct tcpcb *tp);
 
-u_long	 tcp_maxmtu(struct in_conninfo *, struct tcp_ifcap *);
-u_long	 tcp_maxmtu6(struct in_conninfo *, struct tcp_ifcap *);
+uint32_t tcp_maxmtu(struct in_conninfo *, struct tcp_ifcap *);
+uint32_t tcp_maxmtu6(struct in_conninfo *, struct tcp_ifcap *);
 u_int	 tcp_maxseg(const struct tcpcb *);
 void	 tcp_mss_update(struct tcpcb *, int, int, struct hc_metrics_lite *,
 	    struct tcp_ifcap *);