This article considers questions of authorship in Juan Bautista Viseo’s “Second Sermon for Advent” about “frightful, and terrible signs” of Judgment Day. Although Bautista acknowledges important contributions by Nahua scholars in the production of his Nahuatl-language sermonary, he does not plainly recognize them as coauthors. However, the text itself registers indigenous perspectives. This sermon describes several natural phenomena, such as eclipses, comets, floods, windstorms, and earthquakes, as signs of the Apocalypse. For Nahuas, these phenomena similarly foretold disaster or correlated to storied calamities of ages past. Therefore, the sermon refutes ancestral teachings on celestial signs and age-ending cataclysms, distinguishing so-called lies from doctrinal truth. Yet other passages take a heterodox step in the opposite direction, reinforcing connections between Christian and native thought on world time and portents of doom, or citing figurative “signs” of ancestral tradition that speak to the theme of divine judgment. Such passages, this article demonstrates, suggest Nahua co-authorship.