A retainer plate for preventing or at least mitigating loosening of an axle nut of a vehicle. The retainer plate comprises a generally flat section of rigid material that couples to an axle nut in a non-rotatable fashion and to a portion of the wheel to maintain the axle nut in tight threaded engagement with the axle. The retainer plate can have a central bore that non-rotatably engages the axle nut and a radially outward feature that engages the wheel to prevent the axle nut from loosening.