An arrangement in a vehicle engine comprising an intake air manifold, an exhaust gas manifold and a plurality of cylinders, and being adapted for being operated by means of a dual fuel comprising diesel and gas fuel, said arrangement further comprising: an exhaust gas recirculation line connecting said exhaust gas manifold with said intake air manifold, an exhaust gas recirculation valve arranged in said exhaust gas recirculation line, and a control unit arranged for controlling the operation of the exhaust gas recirculation valve, where the arrangement further comprises a knock sensor arranged on said engine and connected to said control unit; said control unit being adapted for opening said exhaust gas recirculation valve in the event that knock is detected by said knock sensor. The advantage of the invention is that a dual fuel engine can be used with methane gas having a wide variety of methane numbers without causing the engine to knock.