An oscillator circuit (100) comprises a crystal oscillator (10) arranged to generate an oscillation signal, a bias current generator (20) arranged to supply a bias current to the crystal oscillator (10), and a feedback stage (30) arranged to generate a feedback signal in response to an amplitude of the oscillation signal reaching an amplitude threshold. The bias current generator (20) is arranged to: in response to a supply of power to the oscillator circuit (100) being switched on, generate the bias current at an increasing level commencing from a first level; in response to the feedback signal, terminate the increasing; and during subsequent oscillation of the crystal oscillator (10), supply the bias current at a second level dependent on a final level of the bias current reached when the increasing is terminated.