--- channels/chan_sip.c	2015-10-09 23:48:48.000000000 +0200
+++ channels/chan_sip.c	2015-11-18 12:56:52.920665892 +0100
@@ -7651,6 +7651,11 @@
 					break;
 			} else {
 				/* Well, if it's not reasonable, just send in-band */
+				if(!ast_test_flag(&p->flags[0], SIP_RINGING)){
+					transmit_provisional_response(p, "180 Ringing", &p->initreq, 0);
+					ast_set_flag(&p->flags[0], SIP_RINGING);
+					break;
+				}
 			}
 		}
 		res = -1;