A selector for an automatically operated gearbox is provided and includes: a casing; a control member mounted within the casing in an oscillating manner around a first axis of rotation, the control member being movable through a plurality of operative positions associated to respective operating conditions of the gearbox; a prevention device of the selection of an undesired operative position of the selector, wherein the prevention device includes a rocker mounted within the casing in a rotatable manner around a second axis of rotation; the rocker being operable in rotation around the second axis of rotation by an actuator member between a resting position and a working position in which it is configured to inhibit the selection of the undesired operative position. The prevention device is configured for enabling, in certain conditions, selection of the undesired operative position even when it is currently inhibited.