Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 140937)
+++ channels/chan_sip.c	(working copy)
@@ -972,6 +972,7 @@
 	int authtries;				/*!< Times we've tried to authenticate */
 	int expiry;				/*!< How long we take to expire */
 	long branch;				/*!< The branch identifier of this session */
+	long invite_branch;         /*!< The branch used when we sent the initial INVITE */
 	char tag[11];				/*!< Our tag for this session */
 	int sessionid;				/*!< SDP Session ID */
 	int sessionversion;			/*!< SDP Session Version */
@@ -5974,7 +5975,10 @@
 		seqno = p->ocseq;
 	}
 	
-	if (newbranch) {
+	if (sipmethod == SIP_CANCEL) {
+		p->branch = p->invite_branch;
+		build_via(p);
+	} else if (newbranch) {
 		p->branch ^= ast_random();
 		build_via(p);
 	}
@@ -7122,6 +7126,7 @@
 	if (init) {		/* Seems like init always is 2 */
 		/* Bump branch even on initial requests */
 		p->branch ^= ast_random();
+		p->invite_branch = p->branch;
 		build_via(p);
 		if (init > 1)
 			initreqprep(&req, p, sipmethod);