Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 233719)
+++ channels/chan_sip.c	(working copy)
@@ -3118,13 +3118,19 @@
 			if (sscanf(p->lastmsg, "Tx: %30s", method_str) == 1 || sscanf(p->lastmsg, "Rx: %30s", method_str) == 1) {
 				if (method_match(SIP_CANCEL, method_str) || method_match(SIP_BYE, method_str)) {
 					p->needdestroy = 1;
+					return 10000;
 				}
 			}
-			return 10000;
+
+			/* Give them twice the maximum interval to respond, then really kill the dialog. */
+			snprintf(p->lastmsg, sizeof(p->lastmsg), "Tx: CANCEL (autodestruct)\n");
+			return (p->timer_t1 < 500 ? 500 : p->timer_t1) * 64 * 2;
 		} else {
 			/* They've had their chance to respond. Time to bail */
 			__sip_pretend_ack(p);
 		}
+		p->needdestroy = 1;
+		p->invitestate = INV_CANCELLED;
 	}
 
 	if (p->subscribed == MWI_NOTIFICATION)
@@ -4523,6 +4529,10 @@
 			ast_queue_control(p->owner, AST_CONTROL_CONGESTION);
 			ast_channel_unlock(p->owner);
 		}
+		p->invitestate = INV_CANCELLED;
+		stop_media_flows(p); /* Immediately stop RTP, VRTP and UDPTL as applicable */
+		p->needdestroy = 1;
+		sip_alreadygone(p);
 	}
 	sip_pvt_unlock(p);
 	return 0;