--- chan_sip.c.orig     2006-12-15 12:41:47.000000000 +0100
+++ chan_sip.c  2006-12-15 12:41:47.000000000 +0100
@@ -9660,6 +9660,8 @@ static void handle_response_invite(struc
        case 100:       /* Trying */
                if (!ignore)
                        sip_cancel_destroy(p);
+
+               ast_set_flag(p, SIP_CAN_BYE);
                check_pendings(p);
                break;
        case 180:       /* 180 Ringing */