(24)When the prospectus is supplemented, harmonisation at Union level of the time-frame for the exercise by investors of the right of withdrawal of their previous acceptances would provide certainty to issuers making cross-border offers of securities. To provide flexibility to issuers from Member States with a tradition of a longer time-frame in this regard, the issuer or the offeror should be able to extend the term for the exercise of that right voluntarily. To improve legal certainty, the supplement to the prospectus should specify when the right of withdrawal ends.