A method for lubricating a gearbox of a wind turbine. The gearbox comprises a plurality of gears and shafts supported by bearings of which at least one bearing is a plain bearing. The gearbox furthermore comprises a lubrication system with both a mechanical pump and an electrical pump for feeding the gears and bearings with lubricant, wherein a difference between a volume capacity of the mechanical and electrical pump is a maximum 40%. The method comprises the step of controlling at least one valve, during start-up of the gearbox, and feeding lubricant to the bearings via the electrical pump; feeding lubricant to the bearings and the gears, during normal operation of the gearbox, via the electrical pump and the mechanical pump; and feeding lubricant only the bearings, during the absence of electrical power supply, via the mechanical pump.