A stopper for a medicament vial including a thin central zone thereof and a beveled sleeve is supported over the outer surface of the thin central zone of the stopper by means of three radially outwardly extending and arched legs anchored to the peripheral portions of the stopper at their outer ends. The sleeve is tapered toward the central area of the stopper and the end of the sleeve adjacent the stopper is beveled for piercing the thin central zone of the stopper. However, the legs support the sleeve with its beveled end at least closely adjacent the stopper and the arched legs are bendable whereby a thrust on the outer end of the sleeve will be sufficient to bend the legs and advance the beveled end of the sleeve toward the central area of the stopper for piercing the same. The sleeve includes an outer barb for retention through the thin central area of the stopper and a conventional aluminum seal is secured over the stopper and the adjacent end of the vial and also covers the stopper piercing sleeve and its bowed support legs.