An auto-injector for administering a dose of a liquid medicament (M) comprises of a substantially cylindrical housing arranged to contain a pre-filled syringe with an injection needle, a plunger and a stopper for sealing a syringe barrel and a drive means releasably coupled to the plunger for advancing the syringe in the proximal direction (P) for needle insertion into an injection site and for displacing the dose of medicament (M) into the injection site. The drive means is arranged to be decoupled from the plunger for advancing a needle shroud to a safe position (PS) to surround the injection needle after the injection. According to the invention, the drive means bears against a thrust collar arranged to be releasably coupled to the plunger through a ramped engagement of a first tongue and a first recess so as to rotate the thrust collar on translation in proximal direction (P). At least one longitudinal gap (G1, G2) is provided for guiding at a first and/or second protrusion of the thrust collar to prevent a rotation of the thrust collar. A circumferential gap (G3) is arranged to allow the thrust collar to rotate out of engagement to the plunger on removal of the auto-injector from the injection site.