--- channels/chan_sip.c	(Asterisk 13.11.2)
+++ channels/chan_sip.c	(working copy)
@@ -17622,6 +17622,7 @@ static enum check_auth_result register_v
 			set_peer_nat(p, peer);
 
 			ast_copy_flags(&p->flags[0], &peer->flags[0], SIP_NAT_FORCE_RPORT);
+			ast_copy_flags(&peer->flags[0], &p->flags[0], SIP_NAT_RPORT_PRESENT);
 
 			if (!(res = check_auth(p, req, peer->name, peer->secret, peer->md5secret, SIP_REGISTER, uri2, XMIT_UNRELIABLE))) {
 				sip_cancel_destroy(p);