The present invention relates to an injector for preventing accidental needle sticks comprising: -a cylinder extending along a longitudinal axis, an inner wall and an outer wall, the cylinder having an outlet at an outlet end opposite an actuating end and a finger grip on the outer wall, which finger grip is positioned between the outlet end and the actuating end, -a piston having a piston body and a deformable sealing element, which deformable sealing element abuts the inner wall of the cylinder at an abutting interface and seals an annular gap between the piston body and the inner wall of the cylinder when the piston is inserted in the cylinder, -a needle guard for mounting on the outside of the cylinder from the outlet end or the actuating end, which needle guard comprises a barrel with a mounting end opposite an operating end, the barrel having a slot for receiving the finger grip of the cylinder when the needle guard is mounted on the cylinder, which slot extends from the mounting end towards the operating end, wherein when the needle guard is mounted on the cylinder from the actuating end in a protective position, the barrel extends along the longitudinal axis and projects beyond the outlet end of the cylinder so that when a hypodermic needle is attached at the outlet end, the barrel protects a user from accidental needle sticks.
