Abstract: 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 cartridge's 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).