A turnbuckle lock for use on a thin-walled door includes a locking tongue and actuating mechanism that are formed as one piece with one another. An inner seal disposed between the housing and actuating mechanism is formed by being sprayed onto the housing. The actuating member and the housing member enclosing the actuating mechanism are permanently connected to each other, and the inner seal is placed inside at least one free space formed on the actuating mechanism. The inner seal and outer seal also may be formed as a one-piece element. By the permanent connection of the housing and the component made up of the actuating mechanism and the locking tongue, it is ensured that the locking tongue cannot be detached from the actuating mechanism, so that the locking function of the turnbuckle lock is always provided.