An injection device comprising a housing and a cap 16 removably mounted over a forward end of the housing. Extending from a rear edge 17 of the cap is at least one slot 50 which engages with a protrusion 30 on an outer surface of the housing. A rearward portion of the cap includes rearwardly extending engagement features 70 provided on each side of the slot which locate within a cavity 60 in the housing when the cap is mounted on the housing. The cavity has corresponding surfaces which align with the cap engagement features to prevent, or limit, the side walls of the slot from splaying outwardly when the cap engagement features are located within the cavity.
