Martyrologium Romanum (Vatican Press, 2001, ISBN978-88-209-7210-3), p. 587. Nicholas was added to the list of saints by Cardinal Lambertini - see F. Bougard, 'Anastase le bibliothécaire ou Jean Diacre ? Qui a récrit la vie de Nicolas Ier et pourquoi ?', Vaticana et medievalia. Études en l’honneur de Louis Duval-Arnould, Jean-Marie Martin, Bernadette Martin-Hisard e Agostino Paravicini Bagliani (ed.), Firenze, Sismel, 2008 (Millennio medievale, 71 ; Strumenti e studi, n.s., 16), pp. 27-40, p. 8 (online http://www.rmoa.unina.it/333/1/RM-Bougard-Diacre.pdf)