Controlling a compression release brake

A method and a system are described for a compression release brake in an engine comprising an exhaust manifold connected to a turbine provided with a variable turbine geometry wherein said turbine is further connected to a back pressure valve for controlling the pressure drop over said turbine wherein the method comprises the steps of: controlling said back pressure valve on the basis of a measured engine speed and a desired braking power; calculating a desired exhaust manifold gas pressure on the basis of said measured engine speed and said desired braking power; and, controlling said variable turbine geometry such that the difference between a measured exhaust manifold gas pressure and said calculated desired exhaust manifold gas pressure is minimized.