a vacuum operated brake power booster including a retaining member for securing the edge bead of a moveable wall diaphragm of the booster to the booster control valve is disclosed . the booster includes a casing subdivided into two chambers by a moveable wall having a diaphragm which has an internal edge bead disposed in an annular groove in the control valve housing of the booster . an annular retention ring surrounds the bead of the diaphragm to the outside of the bead and radially retains the edge bead within the control valve housing groove .