A device for recovering the waste heat energy having a Clausius-Rankine circuit with a line system conveying a working medium via which at least one vaporizer for vaporizing the working medium, an expansion device for expanding the vaporized working medium to produce mechanical work, a condenser for fluidizing the vaporized and expanded working medium as well as a delivery pump for condensing and conveying the working medium through the line system are fluidically connected to one another. A compensation tank supplies additional working medium volume and is connected to a fluid line and can be fluidically separated from the line system via a valve that is controllable via a control device connected to a sensor for detecting working medium temperature and/or pressure, such that a working medium volume is transferred from the compensation tank into the line system or from the line system into the compensation tank.