Hypodermic syringe having a barrel which with an inner wall thereof defines a reservoir, a closing-off device near the first end of the barrel, and a plunger that is movably placed in the second end of the barrel, wherein the closing-off device comprises a circumferential wall that sealingly abuts the inner wall of the barrel, at the side facing away from the nozzle is provided with a recess extending along a centre line of the closing-off device and over the full width thereof, which recess merges into the through-opening, with in the recess two diametrically opposite flexible locking members, extending in the longitudinal direction of the recess and towards the inner wall, which locking members engage into diametrically placed locking grooves in the inner wall, and at the side facing away from the nozzle, at a circumferential part of the closing-off device situated outside of the recess, is provided with two diametrically opposite and radially outwardly extending blocking members, that engage in diametrically placed blocking grooves in the inner wall.