The present invention relates to a medical device for trans-dermal infusion of a medicament. The medical device comprises a reservoir for holding a medicament to be infused and a pump for pumping medicament from the reservoir. The device is assembled or adapted to be assembled in at least one pre-operational arrangement with or without the reservoir and is adapted to be rearranged from the at least one pre-operational arrangement into an operational arrangement comprising the reservoir. In particular, in the pre-operational arrangement without reservoir, the pump is in a mechanically distressed condition preventing functional operation of the pump. In the pre-operational arrangement comprising the reservoir, the pump is in a mechanically distressed condition preventing functional operation of the pump and/or the reservoir is fluidically disconnected from the pump. In the operational arrangement, the pump is in a mechanically stressed condition enabling functional operation of the pump and the reservoir is fluidically connected to the pump.