A locking device for a fold-over backrest of a seat, has a locking housing in which a handle is pivotable between a locked position and an unlocked position, by which handle a pawl of a locking mechanism can be carried between a locked position and an unlocked position. A blocking bolt is movable manually by a closable lock between a blocked position blocking the handle and a released position releasing the handle. A transmission element is driveable displaceably in a guide from a first end position into a second end position. The transmission element has a retaining element and, upon movement of the handle out of the locked position, is movable into a retaining recess of the blocking bolt and prevents the blocking bolt from being able to move from the released position into the blocked position.