The present invention relates A needle assembly for a drug delivery device comprising:- a cup-shaped receptacle (14) of non-circular cross section having a bottom section (16) supporting a needle element (20) being adapted to penetrate a pierceable seal of a cartridge to be disposed in a cartridge holder (10) of the drug delivery device,- wherein the receptacle (14) comprises fastening means (26, 27) adapted to engage with fastening means (24, 25) of a support section (11) of the cartridge holder (10) for releasably fastening the needle assembly,- wherein the fastening means (24, 25, 26, 27) are convertible into a release configuration by changing the radial distance of mutually corresponding fastening means (24, 25, 26,27) through twisting the receptacle (14) with respect to the support section (11).
