A power-assisted braking system for a vehicle is described, including: a brake master cylinder having a chamber which is hydraulically connected to a wheel brake cylinder for braking a wheel of the vehicle; a hydraulic actuator which activates a piston of the brake master cylinder in order to pressurize the hydraulic fluid in the chamber; a low-pressure accumulator which stores the hydraulic fluid under pressure, and the actuator for activating the piston of the brake master cylinder; a pump which supplies the hydraulic fluid from the tank to the low-pressure accumulator; and a drive device which drives the pump. A method for controlling a power-assisted braking system is also described.