A hydraulic brake system includes a brake actuating element, a simulation device with a detector for detecting brake actuation by a driver. No mechanical and/or hydraulic operative connection between the brake actuating element and the wheel brakes is provided. A pressure medium reservoir, an electrically controllable pressure source for actuating the wheel brakes can be connected to each of the wheel brakes, electrically actuable wheel valves assigned to the wheel brakes for setting wheel brake pressures, and at least one electronic control and regulating unit for actuating the pressure source and wheel valves. The pressure source includes at least one piston which is sealed in a housing by a first sealing element and a second sealing element. In the case of a leak of the first sealing element, a pressure build-up is carried out at the wheel brakes by the pressure source with use of the second sealing element.