In a locking device for a camshaft adjuster comprising a drive housing with a rotor with spaced rotor vanes disposed in the drive housing between circumferentially spaced axial walls projecting radially inwardly so as to form operating chambers at opposite sides of the rotor vanes to which hydraulic fluid can be selectively admitted for controlling the relative angular position between the rotor to which a camshaft is connected and the drive housing which is driven by the crankshaft of the engine, wherein locking bolts are provided for interlocking the drive housing and the vane rotor and disposed in one of the housing and the rotor elements while a recess is formed in the other for receiving the locking bolt in order to interlock the drive housing and the vane rotor, the locking bolt is arranged in the hydraulic fluid supply path to the operating chambers upstream of the operating chamber in such a way that hydraulic fluid admission to the operating chambers is controlled by the locking bolt and is admitted to the operating chambers by the movement of the locking bolt to the release position.