A tandem master cylinder for hydraulic brake systems of automotive vehicles. The push-rod piston (29) and the floating piston (34) both are provided with a central valve. The central valve of the push-rod piston is coupled to the floating piston. The length of the bore (28) of the central valve in the push-rod piston (29) is dimensioned to allow the valve closure member (27) of the central valve in the push-rod piston to travel a distance within the bore of the central valve at least equal to the stroke of the floating piston (34).