A ring (10) for disposing around a valve body (21) of an aerosol dispenser valve (20) that is mounted by a fastener element (50), such as a crimpable capsule, on a reservoir (1) containing fluid to be dispensed. The ring (10) includes at least an outer portion (15) and an inner portion (11, 11′) that co-operates with the valve body (21). The ring (10) is made as a single piece that is substantially rigid, the outer portion (15) being adapted to co-operate in leaktight manner, by deformation of its material, with a portion of the reservoir (1) while the fastener element (50) is being assembled on the reservoir (1).