Abstract: A device is disclosed which is mounted to a door over an independently mounted lock to prevent separation of the lock from the door. In one embodiment, the device comprises an interior plate having a recessed portion and flange portions, which is fastened to the interior of the door by bolts passing through the door with the recessed portion covering the lock. The plate holds the lock against the interior of the door and prevents its separation from the door when forces are applied to the lock from the exterior of the door via the lock cylinder or directly to the lock after the cylinder has been removed. In another embodiment, the device also comprises an exterior plate mounted to the exterior of the door covering the heads of the bolts used to mount the interior plate to the door.