Abstract: The invention relates to a fixing device (1), for a multipolar magnetic ring (10) on a gear (20), driven in axial rotation by an electric motor and, in particular, on a motor reducing gear. The invention is characterised in that the fixing device (1) comprises at least one stop element (22a, 22b), fixed to the gear (20), which can engage with an anchor projection (12a, 12b) on the magnetic ring (20), with a coupling direction essentially parallel to the plane of the gear (20), with at least one retaining clip (23) on the gear (20), which engages with a retaining projection (13) on the magnetic ring (20), after elastic deformation, with a coupling direction essentially perpendicular to the plane of the gear (20).