A vacuum brake servo includes a force input element, a control valve actuated by the force input element, a vacuum chamber connected to a vacuum source, and an operating chamber which, depending on the actuation of the force input element, can be connected to either the vacuum chamber or the surrounding atmosphere. The control valve has a control piston that can be actuated by the force input element and, together with a valve element, forms a seal seat having a seal seat diameter between the operating chamber and the surrounding atmosphere. In the area close to the seal seat, a guide channel is provided. When the seal seat is opened, air from the surrounding atmosphere flows into the operating chamber. The guide channel extends axially with a constant flow diameter over a predetermined length, wherein the flow diameter is less than or equal to the seal seat diameter.