The present invention relates to a drug delivery device for dispensing of a dose of a medicinal product, comprising: a first housing component (12, 52 62) adapted to receive a cartridge (16) comprising the medicinal product and further comprising a piston (18) slidably arranged therein in an axial direction, a second housing component (14 54 64) adapted to receive a dose dispensing mechanism having a piston rod (20) to be operably engaged with the cartridges piston (18), wherein the first and the second housing components (12, 14 52, 54 62, 64) are displaceably arranged in axial direction relative to each other for reducing an axial distance (34) between the piston (18) and the piston rod (20) to a pre-defined degree, and an interlock means (30) adapted to interact with at least one of first and second housing components (12, 14 52, 54 62, 64) for mutually locking into position first and second housing components (12, 14 52, 54 62, 64).
