The present invention provides an injection needle unit (10) comprising: a needle assembly (20) comprising: an injection needle (25) extending along a longitudinal axis and having a distal needle end configured for insertion into a subject and a proximal needle end configured for penetration of a reservoir septum, and a skirt (22) surrounding the proximal needle end and defining a receiving space (28) for reception of a needle mount of a drug delivery device, the skirt (22) comprising a slot (24), and a block structure (32) supported exteriorly of the skirt (22), wherein the block structure (32) is biased towards the longitudinal axis and is capable of radial displacement through the slot (24) from a latched position outside the receiving space (28) to a released position within the receiving space (28).
