A sub-assembly for a medicament delivery device including a housing, a propellant source contained in and axially moveable relative to said housing, and a button axially moveable relative to said housing. At least part of said button is disposed axially rearwardly of part of said propellant source. The button includes one or more radially flexible blocking members, and the button is moveable between a first axial position in which the one or more radially flexible blocking members are radially restrained by the housing in a radially inward position that limits rearward axial movement of the propellant source, and a second axial position in which the one or more radially flexible blocking members are able to flex to a radially outward position and permit rearward axial movement of the propellant source relative to the button and the housing.
