Abstract: An actuator having controlled blocking of an end position and a method for operating a parking brake having such an actuator. The blocking device according to the present disclosure is intended to be constructed to be very wear-resistant and fracture-resistant and the force transmission path of the blocking device is not intended to be directed via the electromagnet which actuates the blocking device. The electromagnet in the state supplied with current presses a blocking cone into a piston counter to a spring by means of a tappet, wherein the blocking cone presses a group of balls which are supported in openings of the piston outwards by means of a conical face and wherein these balls are supported, on the one hand, on a shoulder of a blocking sleeve which is connected to a cylinder and, on the other hand, on the openings of the piston and thereby block a movement of the piston out of the end position thereof. Such a system can be used on vehicles having an electrohydraulically actuated parking brake.