A locking sleeve (17) is described for fastening a closure device (11) on a container opening comprising a sleeve body which is at least provided with a slip-on collar at its lower end region, wherein the slip-on collar has an inner circumferential surface (21) for enveloping coverage of an outer circumferential surface (25) of the closure device, this inner circumferential surface being provided with a retaining device (22) at least in an area of overlap with the outer circumferential surface and the retaining device comprising a plurality of retaining units (23) which are radially distributed over the circumference of the inner circumferential surface.