Index: sys/dev/if_wg/module/if_wg_session.c
===================================================================
--- sys/dev/if_wg/module/if_wg_session.c
+++ sys/dev/if_wg/module/if_wg_session.c
@@ -359,8 +359,6 @@
 	struct sockaddr_in6 *sin6;
 	struct ifnet *ifp;
 
-	if (so->so_port == 0)
-		return (0);
 	td = curthread;
 	bzero(&laddr, sizeof(laddr));
 	ifp = iflib_get_ifp(sc->wg_ctx);
@@ -374,6 +372,19 @@
 		if_printf(ifp, "can't bind AF_INET socket %d\n", rc);
 		return (rc);
 	}
+
+	if (so->so_port == 0) {
+		rc = sosockaddr(so->so_so4, (struct sockaddr **)&sin);
+		if (rc != 0) {
+			if_printf(ifp,
+			    "can't fetch listening port from socket, error %d\n",
+			    rc);
+			return (rc);
+		}
+
+		so->so_port = ntohs(sin->sin_port);
+	}
+
 	sin6 = &laddr.in6;
 	sin6->sin6_len = sizeof(laddr.in6);
 	sin6->sin6_family = AF_INET6;
Index: sys/dev/if_wg/module/module.c
===================================================================
--- sys/dev/if_wg/module/module.c
+++ sys/dev/if_wg/module/module.c
@@ -179,13 +179,11 @@
 		err = EBADMSG;
 		goto out;
 	}
-	if (!nvlist_exists_number(nvl, "listen-port")) {
-		device_printf(dev, "%s listen-port not set\n", __func__);
-		err = EBADMSG;
-		goto nvl_out;
-	}
-	listen_port = nvlist_get_number(nvl, "listen-port");
 
+	/* wg_socket_bind() will update with the chosen port if omitted. */
+	listen_port = 0;
+	if (nvlist_exists_number(nvl, "listen-port"))
+		listen_port = nvlist_get_number(nvl, "listen-port");
 	if (!nvlist_exists_binary(nvl, "private-key")) {
 		device_printf(dev, "%s private-key not set\n", __func__);
 		err = EBADMSG;