A device for controlling the compression rate of a variable compression ratio engine comprises: an actuating cylinder comprising a piston defining two chambers for receiving a pressure fluid, a pressure accumulator supplying the pressure fluid, a first fluid circuit connecting the upper chamber to the accumulator and comprising a first valve assembly for controlling the flow of the fluid in the first fluid circuit, and a second fluid circuit connecting the lower chamber to the accumulator and comprising a second valve assembly for controlling the flow of a fluid in the second fluid circuit. At least one of the fluid circuits comprises a bypass conduit arranged so as to connect one of the chambers to the accumulator. The bypass conduit comprises a non-return valve.