A fastener system for releasably fastening a dispenser member on a reservoir neck, the system having a fastener ring including flexible axial tabs for fastening around the reservoir neck, the tabs separated by axial slots; and a locking sleeve engaged around the fastener ring to lock the tabs in engagement around the neck. The sleeve forms a plurality of locking sectors that engage the tabs to lock them around the neck and a plurality of non-locking sectors not in contact with the ring. The sleeve is movable about the ring between an assembled position and a disassembled position in which the locking sectors are situated at the slots so as to enable the tabs to deform in order to disengage from the neck.