A method for operating a high-voltage on-board power system of a motor vehicle is proposed, in which the following steps are carried out: (a) generating a coupling signal for coupling a fuel cell of the vehicle to the on-board power system; (b) carrying out steps c) to f) depending on the coupling signal; (c) activating the fuel cell depending on the coupling signal; (d) determining a current operating voltage of the fuel cell; (e) adjusting an operating voltage of the high-voltage on-board power system decoupled from the fuel cell to the operating voltage of the fuel cell; and (f) coupling the fuel cell to the high-voltage on-board power system.