Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 62624)
+++ channels/chan_sip.c	(working copy)
@@ -3375,6 +3375,7 @@
 					   INVITE, but do set an autodestruct just in case we never get it. */
 					needdestroy = 0;
 					sip_scheddestroy(p, DEFAULT_TRANS_TIMEOUT);
+					p->invitestate = INV_CANCELLED;
 				}
 				if ( p->initid != -1 ) {
 					/* channel still up - reverse dec of inUse counter
@@ -3387,6 +3388,7 @@
 					transmit_response_reliable(p, res, &p->initreq);
 				else 
 					transmit_response_reliable(p, "603 Declined", &p->initreq);
+				p->invitestate = INV_TERMINATED;
 			}
 		} else {	/* Call is in UP state, send BYE */
 			if (!p->pendinginvite) {
@@ -14114,7 +14116,18 @@
 		
 	check_via(p, req);
 	sip_alreadygone(p);
-	p->invitestate = INV_CANCELLED;
+	/* At this point, we could have cancelled the invite at the same time
+		as the other side sends a CANCEL. Our final reply with error code
+		might not have been received by the other side before the CANCEL
+		was sent, so let's just give up retransmissions and waiting for
+		ACK on our error code. The call is hanging up any way. */
+	if (p->invitestate == INV_TERMINATED) {
+		/* This call is already either in UP state or dead */
+		/* Stop any retransmissions that is going on at this time */
+		__sip_pretend_ack(p);
+	};
+	if (p->invitestate != INV_TERMINATED)
+		p->invitestate = INV_CANCELLED;
 	
 	if (p->owner && p->owner->_state == AST_STATE_UP) {
 		/* This call is up, cancel is ignored, we need a bye */
@@ -14129,7 +14142,7 @@
 		ast_queue_hangup(p->owner);
 	else
 		sip_scheddestroy(p, DEFAULT_TRANS_TIMEOUT);
-	if (p->initreq.len > 0) {
+	if (p->initreq.len > 0) {	/* This is a new dialog */
 		transmit_response_reliable(p, "487 Request Terminated", &p->initreq);
 		transmit_response(p, "200 OK", req);
 		return 1;