Parking brake system for a commercial vehicle, comprising - an electronic control unit, - a parking brake valve device suitable for making a first pressure available directly or indirectly, - a service brake valve suitable for making a second pressure available directly or indirectly, - a relay valve having a control inlet, to which the first or the second pressure can be applied, an operating inlet connected to a compressed air reservoir of the commercial vehicle and an operating outlet connected to at least one spring pressure chamber of a combination cylinder (18, 20), - a control valve having a first compressed air inlet, a second compressed air inlet and a compressed air outlet connected to the control inlet of the relay valve, wherein the first pressure can be fed to the first compressed air inlet and the second pressure can be fed to the second compressed air inlet and wherein the higher of the pressures applied to the compressed air inlets (42, 44) is applied to the compressed air outlet, characterised in that - the parking brake valve device is a parking brake valve, and - the parking brake system further comprises: - a valve device located between the parking brake valve and the control inlet of the relay valve and electrically switchable by the electronic control unit, - wherein, in the presence of a person for driving the commercial vehicle, an electrically evaluable indicator can be made available by the electronic control unit, and - wherein the electronic control unit is suitable for preventing a ventilation of the spring brake cylinder (18, 20) by means of the electrically switchable valve device in the absence of the indicator. - an electronic control unit, - a parking brake valve device suitable for making a first pressure available directly or indirectly, - a service brake valve suitable for making a second pressure available directly or indirectly, - a relay valve having a control inlet, to which the first or the second pressure can be applied, an operating inlet connected to a compressed air reservoir of the commercial vehicle and an operating outlet connected to at least one spring pressure chamber of a combination cylinder (18, 20), - a control valve having a first compressed air inlet, a second compressed air inlet and a compressed air outlet connected to the control inlet of the relay valve, wherein the first pressure can be fed to the first compressed air inlet and the second pressure can be fed to the second compressed air inlet and wherein the higher of the pressures applied to the compressed air inlets (42, 44) is applied to the compressed air outlet, characterised in that - the parking brake valve device is a parking brake valve, and - the parking brake system further comprises: - a valve device located between the parking brake valve and the control inlet of the relay valve and electrically switchable by the electronic control unit, - wherein, in the presence of a person for driving the commercial vehicle, an electrically evaluable indicator can be made available by the electronic control unit, and - wherein the electronic control unit is suitable for preventing a ventilation of the spring brake cylinder (18, 20) by means of the electrically switchable valve device in the absence of the indicator.