A hydraulic brake booster comprises a housing forming a pressure chamber and a pair of bores leading to the pressure chamber. One of the bores receives an output piston and the other bore receives a valve member. The valve member is movable by an input actuator to control communication of fluid pressure to the pressure chamber. The end of the valve member within the pressure chamber carries a sleeve and a poppet. The sleeve resiliently imparts movement to the valve member and the poppet cooperates with the sleeve to close communication to the pressure chamber in response to movement of the sleeve relative to the valve member.