Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 355999)
+++ channels/chan_sip.c	(working copy)
@@ -10354,10 +10354,14 @@
 
 	add_header(req, "Via", p->via);
 	/*
-	 * Use the learned route set unless this is a CANCEL. For a CANCEL
-	 * we have to send to the same destination as the original INVITE.
+	 * Use the learned route set unless this is a CANCEL on an ACK for a non-2xx
+	 * final response. For a CANCEL or ACK, we have to send to the same destination
+	 * as the original INVITE.
 	 */
-	if (p->route && sipmethod != SIP_CANCEL) {
+	if (sipmethod == SIP_CANCEL ||
+			(sipmethod == SIP_ACK && p->invitestate == INV_COMPLETED)) {
+		set_destination(p, ast_strdupa(p->uri));
+	} else if (p->route) {
 		set_destination(p, p->route->hop);
 		add_route(req, is_strict ? p->route->next : p->route);
 	}