diff --git a/sys/netinet6/in6.h b/sys/netinet6/in6.h
index 5691dc3eab12..af3711dcfb7a 100644
--- a/sys/netinet6/in6.h
+++ b/sys/netinet6/in6.h
@@ -532,7 +532,7 @@ struct in6_pktinfo {
  */
 struct ip6_mtuinfo {
 	struct sockaddr_in6 ip6m_addr;	/* or sockaddr_storage? */
-	u_int32_t ip6m_mtu;
+	uint32_t ip6m_mtu;
 };
 
 /*