An engagement element is provided on the inside of the door leaf or of the door at a defined distance from the inside of the door. A spring-loaded locking hasp lies horizontally opposite the engagement element on the inside of the door frame. The locking hasp has a semicircular or claw-shaped recess and a laterally projecting locking section. A locking element is movably guided inside the door frame and connected to a vertically movable rod. During the closing movement of the door, the engagement element engages with the recess of the locking hasp, which swings with its locking section in the direction of the center of the door opening and assumes a position parallel to the door and is locked in this position by a movement of the locking element which is triggered in the vertical direction.