An autoinjector comprising: a case adapted to hold a medicament container having a needle, the case including an angled rib (2.6); 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, the needle shroud having a first shroud boss (7.2); a plunger slidably disposed in the case and biased relative to the case by a drive spring so as to forward a force of the drive spring to a stopper within a medicament container, the plunger including a plunger boss (10.1); wherein the plunger boss (10.1) abuts the rib (2.6) when the plunger is biased against the rib (2.6) for rotating the plunger boss (10.1), wherein the first shroud boss (7.2) is arranged to abut the plunger boss (10.1) and prevent it from disengaging the angled rib (2.6) when the first shroud boss (7.2) is axially aligned with the angled rib (2.6) in the extended position of the needle shroud and wherein the plunger boss (10.1) disengages the rib (2.6) when the needle shroud is in the retracted position thereby axially misaligning the first shroud boss (7.2) with the plunger boss (10.1) such that the plunger boss (10.1) rotates due to being biased in the distal direction towards the angled rib such that the plunger boss (10.1) comes clear of the angled rib (2.6) to allow the plunger to translate axially relative to the case, characterized in that the rib (2.6) is angled with respect to a longitudinal axis of the case and imparts a rotational and an axial force on the plunger boss (10.1). a case adapted to hold a medicament container having a needle, the case including an angled rib (2.6); 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, the needle shroud having a first shroud boss (7.2); a plunger slidably disposed in the case and biased relative to the case by a drive spring so as to forward a force of the drive spring to a stopper within a medicament container, the plunger including a plunger boss (10.1); wherein the plunger boss (10.1) abuts the rib (2.6) when the plunger is biased against the rib (2.6) for rotating the plunger boss (10.1), wherein the first shroud boss (7.2) is arranged to abut the plunger boss (10.1) and prevent it from disengaging the angled rib (2.6) when the first shroud boss (7.2) is axially aligned with the angled rib (2.6) in the extended position of the needle shroud and wherein the plunger boss (10.1) disengages the rib (2.6) when the needle shroud is in the retracted position thereby axially misaligning the first shroud boss (7.2) with the plunger boss (10.1) such that the plunger boss (10.1) rotates due to being biased in the distal direction towards the angled rib such that the plunger boss (10.1) comes clear of the angled rib (2.6) to allow the plunger to translate axially relative to the case, characterized in that the rib (2.6) is angled with respect to a longitudinal axis of the case and imparts a rotational and an axial force on the plunger boss (10.1).