In a camshaft adjuster for an internal combustion engine comprising a blade wheel, which is rotationally connected to a camshaft and which is mounted in a driving part so as to be able to rotate in a limited manner, starting from an inner base circle and extending to an outer peripheral circle, the blade wheel, with its blades, engages inside intermediate spaces formed by radial projections of the driving part. A pressure chamber is formed in the peripheral direction on both sides of a blade and can be supplied with pressure oil via a control valve so that the blade wheel is displaced relative to the driving part about an angle according to the pressure ratios existing inside the pressure chambers. In addition, a locking bolt, which can be hydraulically unlocked and which is subjected to the action of a pressure spring in a locking direction, may lock the blade wheel to the driving part. The locked position is situated between two end positions of the blade wheel. After a startup phase, the bolt is firmly held disengaged by a pressurized system fluid to safely prevent locking of the bolt.