A safety-binding heelpiece, for a ski boot, comprising a tubular body (1) having a trigger function and including, at one of its ends, a heel grip (2) for holding the heel of a ski boot on a ski, this tubular body (1) being articulated in rotation about a cam (3) formed in a cylindrical piece, this cam being integral with two lateral arms (4) connected to a base (8) mounted so as to move longitudinally on a plinth (9) for fasting to a ski, the separation between the two arms (4) at the base being smaller than their separation at their link with the cam.