A mechanism for winding a timepiece including at least first and second energy accumulators, the winding mechanism including a winding stem, a winding pinion and a sliding pinion having face gear toothings, arranged to allow the winding pinion to be driven by the sliding pinion in both directions of rotation of the winding stem, the winding stem and the sliding pinion occupying the same axial winding position. The winding stem is housed inside a bottom plate so that the winding pinion is operational on either side of the winding stem with respect to the bottom plate and the winding mechanism includes first and second coupling/uncoupling devices arranged on either side of the winding stem with respect to the bottom plate.