An operating method is provided for a fuel cell system, in particular a fuel cell system in a motor vehicle. The system includes a cooling system via which waste heat of fuel cells of the fuel cell system is ultimately dissipated into the surrounding air, and a tank withstanding an internal pressure of the order of 150 bar and more. In the tank, fuel for the fuel cell system is stored in the cryogenic state, in particular as a cryogen, which tank has a heat exchanger in its storage volume, via which, in order to compensate for the pressure reduction resulting from the removal of fuel from the tank, heat can be supplied to the stored fuel in a controlled manner by way of a heat transfer medium. At operating points or in operating states of the fuel cell system in which the waste heat of the fuel cell system cannot be dissipated to the surroundings to the required extent, at least a portion of the waste heat from the fuel cells is supplied to the heat exchanger in the tank storing the fuel until a predefined limit value for the internal pressure in the tank is reached.