The invention concerns a syringe provided with a body (1), a piston (6) capable of sliding in the body (1), and an injection device comprising a needle (19) oriented along a longitudinal axis (15) and a casing (8) removably secured to the body and carrying said needle (19), the casing (8) comprising a plurality of flexible tabs, each provided with a stop (12), the piston comprising a docking system provided with a housing that comprises a flange configured to hold the stops (12) of the flexible tabs in the housing in an insertion position in which the tabs are inserted into the housing, the plurality of tabs comprising a first tab (16) and a second tab (17) situated in opposing areas around the longitudinal axis (15), the flange comprising a first bearing area (22) and a second bearing area (23) configured to be in contact respectively with the first tab (16) and the second tab (17) in the insertion position. The first tab (17) and the second tab (17) are configured to exert an elastic pressure respectively on the first bearing area (22) and the second bearing area in the insertion position, and the first bearing area (22) and the second bearing area (23) are dissymmetrical relative to the longitudinal axis (15).
