An arrangement for mixing a first and a second gas flow, for example, an inlet flow with an exhaust gas return flow in a diesel engine. An air conduit has an inlet for the first flow and an inlet for the second flow, in order to achieve the mixing. A valve body is arranged to be displaced in the longitudinal direction of the air conduit at the inlet for the second flow in order to achieve a variable venturi effect and in this way a variable suction effect and mixture of the mixed flow. One or more fuel injectors inject fuel into the air conduit to pre-mix fuel with the first and second gas flows before reaching the engine cylinders for combustion.