A medicament delivery device comprising: a housing for receiving a syringe, the housing having first and second casing parts (14, 16) separably attachable to one another; a sleeve receivable within the housing and comprising a tubular wall having an inner surface delimiting a bore and an opposing outer surface; and a locking member receivable and retainable within the second casing part such that the locking member is axially movable between first and second axial positions relative to the second casing part, the locking member comprising a body portion having one or more radially inward protrusions extending therefrom such that: in the first axial position the one or more radially inward protrusions is engageable with the outer surface to inhibit an axial movement of the sleeve relative to the first casing part and radially outward movement of the one or more radially inward protrusions to disengage the one or more radially inward protrusions from the outer surface is inhibited by abutment of the locking member against the second casing part; and in the second axial position radially outward movement of the one or more radially inward protrusions is not inhibited by abutment of the locking member against the second casing part such that the one or more radially inward protrusions is disengageable from the outer surface, wherein the locking member is disengageable from the outer surface by a radially outward movement of the one or more radially inward protrusions into a space radially outward of the locking member. a housing for receiving a syringe, the housing having first and second casing parts (14, 16) separably attachable to one another; a sleeve receivable within the housing and comprising a tubular wall having an inner surface delimiting a bore and an opposing outer surface; and a locking member receivable and retainable within the second casing part such that the locking member is axially movable between first and second axial positions relative to the second casing part, the locking member comprising a body portion having one or more radially inward protrusions extending therefrom such that: in the first axial position the one or more radially inward protrusions is engageable with the outer surface to inhibit an axial movement of the sleeve relative to the first casing part and radially outward movement of the one or more radially inward protrusions to disengage the one or more radially inward protrusions from the outer surface is inhibited by abutment of the locking member against the second casing part; and in the second axial position radially outward movement of the one or more radially inward protrusions is not inhibited by abutment of the locking member against the second casing part such that the one or more radially inward protrusions is disengageable from the outer surface, wherein the locking member is disengageable from the outer surface by a radially outward movement of the one or more radially inward protrusions into a space radially outward of the locking member. in the first axial position the one or more radially inward protrusions is engageable with the outer surface to inhibit an axial movement of the sleeve relative to the first casing part and radially outward movement of the one or more radially inward protrusions to disengage the one or more radially inward protrusions from the outer surface is inhibited by abutment of the locking member against the second casing part; and in the second axial position radially outward movement of the one or more radially inward protrusions is not inhibited by abutment of the locking member against the second casing part such that the one or more radially inward protrusions is disengageable from the outer surface, wherein the locking member is disengageable from the outer surface by a radially outward movement of the one or more radially inward protrusions into a space radially outward of the locking member.