A pneumatic brake booster with a booster housing, which comprises a first and a second housing shell and is subdivided into a working chamber and a vacuum chamber by an axially movable wall to which a pneumatic differential pressure can be applied, with the movable wall being formed of a diaphragm plate and a diaphragm abutting thereon that includes a radially inward sealing bead and a radially outward sealing bead for sealing the two chambers and the radially outward sealing bead is compressible between the housing shells. To improve the compression of the radially outward sealing bead, the radially outward sealing bead has a circumferential, uniform rib structure.