The instant application is directed to an assembly for a drug delivery device which is arranged to operate in two distinct modes, a priming mode starting from a pre-priming state and a dispense mode operating in a post-priming state, and a drug delivery device comprising this assembly. The assembly comprises a dose member, an actuating member and a piston rod which is configured to act on a bung of an assembled cartridge containing the drug. In the pre-priming state the actuating member is configured to be moved by a user such that the movement of the actuating member causes a movement of the dose member and such that the movement of the dose member causes a movement of the piston rod. In the post-priming state the dose member is configured to be moved by a user without causing a movement of the actuating member in order to perform a set and dispense action of the drug delivery device.