An autoinjector includes a case adapted to hold a medicament container having a needle, a needle shroud slidably disposed in the case and translatable between an extended position relative to the case in which the needle is covered and a retracted position relative to the case in which the needle is exposed, and a plunger slidably disposed in the case. The case includes a rib. The plunger includes a plunger boss adapted to abut the rib and the needle shroud when the needle shroud is in the extended position and disengage the rib when the needle shroud is in the retracted position to allow the plunger to translate axially relative to the case.