A sub-assembly of a medicament delivery device is presented, where the sub-assembly includes a plunger rod that is biased, a main body arranged on the plunger rod, and a coupling member movable relative to the main body, where the main body includes a first locking element, the coupling member includes a second locking element, and where the first locking element and the second locking element are configured to be releasably engaged with each other such that the coupling member is prevented from moving relative to the main body.