With the intention of dissuading an unidentified monk from leaving his monastery, Desiderius Erasmus in October 1527 wrote a letter about the blessings of the monastic condition. This letter was last published as Ep. 1887 in volume 7 of P.S. Allen’s edition of Erasmus’ collected letters. The Antwerp University Library, in its Special Collections, contains a hitherto overlooked manuscript witness for this letter, which helps in establishing the relationships among all extant witnesses and allows for a reconstruction of Erasmus’ original letter.