A power-steering system, e.g., for a motor vehicle, having an electric motor, which transmits a steering-assist force via a belt transmission to a ball-screw transmission for displacing vehicle wheels, includes a cam, via which the ball-screw transmission and/or electric motor is supported in a steering-gear housing. The tension of a belt of the belt transmission is adjustable by rotating the cam in the steering-gear housing. The cam has at least one cutout on the circumference, and/or the steering-gear housing has at least one cutout in its inner wall. A locking element may be inserted into the cutout, in order to fix the cam in position with respect to the steering-gear housing. After being inserted, the locking element is operatively connected to the cam and the steering-gear housing.