A compressor diffuser for a vehicle engine turbocharger, the diffuser comprising: a diffuser housing having a gas flow path having a side wall connecting a gas inlet to a gas outlet; a plurality of pivotally mounted diffuser vanes arranged in the flow path to control gas flow, and a vane angle control device for adjusting the angle of each of the plurality of vanes in the flow path; the control device comprising a unison ring coupled to the plurality of vanes in such a way that rotation of the unison ring pivots each of the vanes by interaction of a cam surface with a respective cam follower.