A vane-type camshaft adjuster having a stator, and a rotor connectable to a camshaft. The rotor has a plurality of radially protruding blades inserted in respective blade grooves. The blade groove has groove side faces, a groove bottom and rounded transition regions between the groove side faces and the groove bottom. The transition regions undercut the groove side faces, wherein the rounded transition regions are configured, at least in part, as circular arc segments which undercut the groove bottom.