--- channels/chan_sip.c	(Asterisk 13.38.1)
+++ channels/chan_sip.c	(working copy)
@@ -10857,7 +10857,7 @@ static int process_sdp(struct sip_pvt *p
 	}
 
-	if ((portno == -1) &&
-	    (vportno == -1) &&
-	    (tportno == -1) &&
+	if ((portno == -1 || p->rtp) &&
+	    (vportno == -1 || p->vrtp) &&
+	    (tportno == -1 || p->trtp) &&
 	    (udptlportno == -1)) {
 		ast_log(LOG_WARNING, "Failing due to no acceptable offer found\n");