The present invention is directed to a method for assembling a drug delivery device with a drive mechanism and a bung movably provided in a cartridge. The drive mechanism includes a piston rod and a bearing for driving the bung in a distal direction, wherein the bearing and the piston rod are configured to be connected via a snap connection and wherein the contact between the drive mechanism and the bung is indicated by a detectable signal produced by the engaging snap connection. The method includes the steps of placing the bearing on the bung, displacing the piston rod towards the bearing such that the snap connection is established, monitoring for the signal and stopping displacement of the piston rod upon detection of the signal. The invention is further directed to drug delivery device produced according to the respective method.
