A method for securing a cartridge to a body for a drug delivery device is provided comprising the step of securing the cartridge to the body by means of a releasable connection to prevent accidental relative movement between the cartridge (4) and the body during assembly of the device. Afterwards, the releasable connection is modified irreversably into a non-releasable connection such that the cartridge is permanently secured to the body. Furthermore, an assembly for a drug delivery device is provided comprising a cartridge, a body, a first connection means and a second connection means. The first connection means and the second connection means are configured to mechanically cooperate to form a releasable connection. The releasable connection is suitable for releasably securing the cartridge to the body. The releasable connection prevents accidental relative movement between the cartridge and the body during assembly of the device. The first connection means and the second connection means are irreversably non-releasably secured to each other.