The invention relates to a locking cover (1), made of a molded plastic material, for a vessel having a neck, intended for locking a plug (4) in the neck (3) of the vessel (2), including a wire-cap (6) which surrounds the plug and the neck, a ring (7) which is attached around the wire-cap (6) and shaped so as to have a central opening (17) providing access from the outside of the cover (1) to the inside of the vessel via the plug, and a cap (23) attached to the ring and shaped so as to close said opening (17). The cap (23) comprises attachment tabs (25) which are spaced apart from each other along the annular periphery of the opening (17) of the ring (7) and which are clamped between the ring (7) and the wire-cap (6).