Disclosed is a locking cover (1) for a vessel (2) having a neck (3), intended to fix a stopper (4) in the neck (3) of the vessel (2). The disclosure notes that locking covers are useful in medical applications to prevent irreversible separation of a cap from a cover. The locking cover (1) comprises a cage (6) with locking tabs (8, 9) that is configured to surround the stopper (4) and the neck (3) and to lock them in position relative to each other in a given axial direction (A). A ring (7) is fastened around the cage (6) and is configured with a central aperture (17) that preserves access from outside the cover (1) to the inside of the vessel (2) by way of the stopper (4). A cap (23) is configured to close the aperture (17). The cap (23) has a flat head large enough to cover the aperture (17) and attachment tabs (25) that project substantially perpendicularly relative to the head. The attachment tabs (25) are spaced apart along the annular periphery of the aperture of the ring (7) and are gripped as in a vice between the ring (7) and the cage (6).
