A method for controlling a compressor of a turbocharger is disclosed. In one example, the method comprises varying a maximum permitted compressor outlet temperature based upon a function of compressor outlet temperature and operating time, and controlling the operation of the compressor so that the maximum permitted compressor outlet temperature is not exceeded. In this way a higher boost pressure can safely be used during the early life of the compressor but excessive coking of the compressor with a resultant loss of efficiency later in the life of the compressor is reduced.