An arrangement for a drug delivery device is provided. The arrangement comprises a cap defining a cavity and a body, wherein the cap or the body comprise a recess, wherein the cap or the body is provided with a seal further comprising a sealing surface. When the cap is attached, the sealing surface of the seal seals a section of the cavity. When the cap is detached from the body, either the recess is moved towards the side of the seal which faces the section of the cavity or the seal is moved towards the side of the recess which faces the section of the cavity, and when either at least a part of the recess has passed the sealing surface or, when the sealing surface has passed at least a part of the recess, this part of the recess establishes a passageway between the cavity and the environment.
