A master cylinder for a regulated braking system having at least one piston, which is movable in a housing and which is sealed from a pressure chamber by a sealing element arranged in a ring groove of the housing, which can be connected to an unpressurized supply chamber by control passages designed in the pistons. In order to reduce the flow resistance of the control passages at the same dead stroke, the control passages have a control edge designed parallel to a piston end face of at least one of the pistons.