A method for operating a braking system of a vehicle which is equipped with a plunger device, including the increasing of a brake pressure in at least one brake circuit of the braking system by transferring a brake fluid volume from the plunger device into the at least one brake circuit of the braking system, the method including: comparing an actual pressure variable to a predefined reference pressure variable with regard to an actual pressure present at least in one subsection of the braking system before the brake pressure is increased; and reducing at least a pre-pressure in the braking system prior to transferring the brake fluid volume from the plunger device into the at least one brake circuit if the actual pressure variable exceeds the reference pressure variable. A control unit is also described for a braking system of a vehicle which is equipped with a plunger device.