An auto-injector (1) for administering a dose of a liquid medicament (M) comprises - a substantially cylindrical housing (2) arranged to contain a pre-filled syringe (5) with an injection needle (12), a plunger (9) and a stopper (10) for sealing a syringe barrel (11) and - a drive means (8) releasably coupled to the plunger (9) for advancing the syringe (5) 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 (8) is arranged to be decoupled from the plunger (9) for advancing a needle shroud (3) to a safe position (PS) to surround the injection needle (12) after the injection. According to the invention, the drive means (8) bears against a thrust collar (7) arranged to be releasably coupled to the plunger (9) through a ramped engagement of a first tongue (7.1) and a first recess (6.2) so as to rotate the thrust collar (7) on translation in proximal direction (P). At least one longitudinal gap (G1, G2) is provided for guiding at a first and/or second protrusion (7.2, 7.3) of the thrust collar (7) to prevent a rotation of the thrust collar (7). A circumferential gap (G3) is arranged to allow the thrust collar (7) to rotate out of engagement to the plunger (9) on removal of the auto-injector (1) from the injection site.
