Accessory transmission for an engine of a motor vehicle has a first pulley adapted to be connected to a crankshaft of the engine, a second pulley adapted to be connected to a shaft of an electric machine through a one-way clutch, and a belt connecting the first and the second pulley to one another in order to rotate in one and the same rotation direction (R). The one-way clutch is configured so as to couple the second pulley to the shaft of the electric machine when the electric machine drives the second pulley in the rotation direction, and to decouple the second pulley from the shaft of the electric machine when the second pulley tends to overrun the electric machine in the rotation direction.