The disclosure relates to a drug delivery device for dispensing a liquid drug through a needle with a proximal and a distal needle tip, comprising a body, a needle holder holding the needle relative to the body, a cartridge holder holding a cartridge comprising the liquid drug sealed with a septum on a distal end and with a movable stopper on a proximal end, and a cap adapted to cover at least the distal needle tip of the needle, wherein the cartridge holder is movable relative to the body from a retracted position towards an advanced position, thereby piercing the proximal needle tipthrough the septum, characterized in that the cap is releasably engaged with the cartridge holder, wherein the cap is released from the cartridge holder in its advanced position.