A needle assembly for a drug delivery device includes a cup-shaped receptacle of non-circular cross-section having a bottom section supporting a needle element. The needle element is adapted to penetrate a pierceable seal of a cartridge to be disposed in a cartridge holder of the drug delivery device. The receptacle includes a fastening mechanism adapted to engage with a fastening mechanism of a support section of the cartridge holder for releasably fastening the needle assembly. The fastening mechanisms are convertible into a release configuration by changing the distance between mutually corresponding fastening mechanisms through twisting the receptacle with respect to the support section.