A locking device (1) intended to be movably arranged in relation to an engagement means (3), which locking device comprises a hook bolt (15) for engagement with the engagement means and a control element, which hook bolt presents an aperture (21) with an inner surface, and which control element comprises a follower (27) having an eccentric axis of rotation and a peripheral surface. The control element is arranged to transmit motion from an operating means to the hook bolt when the operating means is moved between a locking position and a release position, so that a relative tightening between the engagement means and the locking device is achieved when the operating means is moved to its locking position. In order to prevent breaking up of the locking device, the hook bolt is provided with a securing surface (17b), which is arranged to turn around the engagement means during locking.