The present disclosure relates to an injection device including: a housing; a carrier disposed within the housing for holding a syringe that has a needle at one end; a needle sleeve located within the housing and being axially moveable with respect to the housing between an extended position and a retracted position; a biasing element configured to bias the needle sleeve towards the extended position; and a locking mechanism configured to lock the needle sleeve in the extended position after use of the injection device, the locking mechanism comprising; a first locking member provided on and projecting from the carrier; and a second locking member comprising a deflectable arm provided on the needle sleeve and moveable between a relaxed position and a deflected position.