The invention relates to a device for locking a nut (13) in a tightened position on a rotary shaft (12), said rotary shaft (12) being hollow at least at one end (14). The locking device comprises a plurality of outer notches (16) formed in a face of the nut (13), said outer notches (16) extending parallel to a longitudinal axis (X) of the nut (13), a plurality of inner notches (15) formed in the end (14) of the rotary shaft (12), said inner notches (15) extending parallel to a longitudinal axis (X) of the rotary shaft (12), and a ring (18) suitable for being installed inside said end (14) of the rotary shaft (12) and presenting at least one first radial finger (19) for being received both in one of the inner notches (15) and in one of the outer notches (16) with the nut (13) being in a tightened position and the two notches (15, 16) housing said first radial finger (19) being at least partially in alignment in a radial direction. In order to balance the ring about a central axis (X), the ring (18) presents an internal outline (21) arranged in such a manner that the barycenter (B) of said internal outline (21) is offset relative to said longitudinal axis (X) when the ring (18) is installed inside the end (14) of the rotary shaft (12).