Provided is a medicament delivery device (100) comprising a tubular housing (110), having a proximal end (111) and an opposite distal end (112), an actuator means (119, 120), slidably and coaxially arranged inside the tubular housing (110) wherein is provided an inter-locking mechanism (119, 413) between the a cap (410) and the housing (110), enabling the cap (410) to freely spin, i.e. it is impossible to open the cap (410), until the medicament delivery device (100) has been properly activated by an activator means (160).