A compressor casing for a turbocharger has an inlet port (6) which communicates with an inlet passage (7), which accommodates an impeller (11) and which communicates with a diffuser (8), which in turn communicates with a scroll (9). An annular chamber (25) is provided between the inlet passage (7) and the scroll (9) and communicates with the inlet passage (7) via a first opening (28) which is directed perpendicular to the impeller axis and optionally also via a second opening (30) which is also directed perpendicular to the impeller axis and is situated upstream of the first opening (28). <IMAGE>
