The invention refers to an arrangement for coupling a plunger (9) to either a syringe (3) or a stopper (6) arranged in the syringe (3), the arrangement comprising a syringe holder (22) which is slidably arranged in a housing (2), wherein the syringe holder (22) is provided with at least one resilient syringe holder arm (23) arranged distally, the syringe holder arm (23) having an inclined surface for bearing against a shoulder (24) , which is arranged at the plunger (9), wherein the syringe holder arm (23) is supportable by an inner surface of the housing (2) in order to prevent it from being flexed outward in a first position and wherein a widened portion (2.1) is provided in the housing (2) for allowing the syringe holder arm (23) to flex outwards and disconnect from the plunger (9) when in a more proximal position so as to switch load of the plunger (9) from the syringe (3) to the stopper (6).
