The invention relates to a door lock or flap lock comprising a locking mechanism that has a rotary latch and a pawl for locking the rotary latch. Said type of lock is also described in DE 103 20 457 A 1. The aim of the invention is to provide a lock with a position securing system with low technical complexity. Said aim is achieved by a lock with a locking mechanism comprising a rotary latch and a pawl for locking the rotary latch. The lock comprises a position securing system for a locking or anti-theft device. A spring is used for securing the position. Said spring is embodied as a dual-acting clamping spring. A tilting mechanism tilts a slot thus securing the position of the slot if excessively accelerated. As a result, an undesired movement of the slot is inhibited and the position thereof is thus improved.