--- asterisk-1.4.19_orig/channels/chan_sip.c	2008-03-26 20:04:35.000000000 +0100
+++ asterisk-1.4.19/channels/chan_sip.c	2008-04-18 08:46:06.000000000 +0200
@@ -12164,8 +12164,22 @@
 			} 
 
 			/* Save Record-Route for any later requests we make on this dialogue */
-			if (!reinvite)
-				build_route(p, req, 1);
+			if (!reinvite) {
+				/* When doing reinvites, after a hangeup, we get the following
+				   exchange:
+				   INVITE ---->
+				   <-------- OK
+				   ACK ------->
+				   However, after the INVITE, sip_hangup() is called, which sets
+				   owner to NULL, causing the test above to think we are not in
+				   a reinvite. To ensure the ack is sent correctly, we have to
+				   catch this situation here. */
+				if (! p->owner && p->invitestate == INV_CONFIRMED)
+					if (sipdebug)
+						ast_log(LOG_DEBUG, "Assuming this is a reinvite for a call we're hanging up.\n");
+				else
+					build_route(p, req, 1);
+			}
 		}
 		
 		if (p->owner && (p->owner->_state == AST_STATE_UP) && (bridgepeer = ast_bridged_channel(p->owner))) { /* if this is a re-invite */