A drive system for a brushless DC motor having a rotor includes at least one permanent magnet and a stator including at least one phase winding. The system has a drive circuit including a switch associated with the winding for varying the current passing through the winding; a rotor position sensor arranged to sense the position of the rotor; and a controller arranged to provide drive signals to control the switch. The drive system is further arranged to receive a temperature signal that has a value dependent upon the temperature of the at least one magnet of the rotor. The controller is arranged to vary the phase of the current passing through the winding relative to the rotor position dependent upon the temperature of the rotor magnet.