(EN) In a compressor of an exhaust gas turbocharger for an internal combustion engine including a compressor wheel which is rotatably mounted in a compressor inlet duct and an auxiliary rotor wheel arranged so as to be movable axially between a coupled position in engagement with the compressor wheel and a decoupled position, disengaged from the compressor wheel, an adjustable guide vane structure is provided which is movable by an adjusting element together with the auxiliary rotor wheel and a contoured flow control ring for controlling the combustion air flow to the compressor wheel and to the auxiliary rotor wheel.