A method for operating a braking system of a motor vehicle equipped with a wheel-slip control device, wherein the braking system includes an electrohydraulic service brake, set to generate braking forces independently of an actuation by an operator. The system having a mechanical or electromechanical parking brake actuated by an actuating element, and acting, in particular, on the rear wheels of the motor vehicle. An operator-side intent to actuate the parking brake is recognized and subsequently during the actuation of the parking brake a hydraulic pressure of the service brake is generated that acts on at least one rear wheel, of the motor vehicle capable of being braked by the parking brake. The hydraulic pressure sufficient to assist the parking brake and correspondingly lock the rear wheel of the motor vehicle braked by the parking brake during travel of the motor vehicle.