A locking element for locking of a panel cover on a module rail includes a bearing block with a flat mounting surface and threaded holes for mounting on the inside of the panel cover and a slide lock, which is mounted to move on the bearing block and has a locking tab. A sliding mechanism moves the slide lock from a locked position, in which the locking tab engages beneath the module rail, to a release position and vice versa. An actuating screw forms a rotary actuator, which can be activated through a hole in panel cover when the locking element is engaged.