A length-adjustable connecting rod for a reciprocating-piston engine. At least one first rod part and second rod part are telescopically displaceable relative to and/or into one another. The second rod part forms a guide cylinder and the first rod part forms a piston element which is longitudinally displaceable in the guide cylinder. Between the first and second rod parts is a high-pressure chamber into which at least one first oil duct opens. At least one control valve is arranged in the first oil duct, with an actuator thereof to be displaced into a first position by a spring and into a second position by oil pressure against the force of the spring. To permit adjustment of the compression ratio, a second oil duct formed as a feed duct opens into the high-pressure chamber and in which a check valve is arranged which opens in the direction of the high-pressure chamber.