A compressor typically for use in a turbocharger comprises a downstream radial compressor impeller wheel, an upstream axial compressor impeller wheel and an intermediate stator. The compressor housing has an inlet with inner and outer walls that define between them an MWE gas flow passage. An upstream opening defined by the flow passage provides communication between the passage and the intake and at least one first slot downstream of the upstream opening provides communication between the passage and the inner surface of the inner wall. The stator comprises a plurality of fixed vanes and is disposed in the inner wall of the inlet between the radial and axial impeller wheels. The position of the slot can be at one of several positions along the gas flow passage, in other embodiments there are second and third slots and the flow passage is divided into two parts. All the arrangements are designed to improve the compressor map width.