26 CFR 301.6501(n)-3: (n)-3 Certain set-asides described in section 4942(g)(2).

Where a deficiency of tax of a private foundation results from the failure of an amount set aside by such foundation for a specific project to be treated as a qualifying distribution under section 4942(g)(2)(B)(ii)(II), such deficiency may be assessed within two years after the expiration of the period within which a deficiency may be assessed for the taxable year to which the amount set aside relates.