In the civil war of 1341–1347 he remained loyal to Andronikos III's under-age son, John V Palaiologos, and opposed Kantakouzenos; as a reward, he was raised to the post of "megas stratopedarches" on the occasion of John V's coronation on 19 November 1341. One of his nieces even became the second wife of one of the chief leaders of John V's regency council, Alexios Apokaukos, but in late 1342 Choumnos fell out with Apokaukos when he pleaded in favour of making peace with Kantakouzenos, and was placed under house arrest. He is possibly to be identified with a monk named Gerasimos Choumnos, which would indicate that at some point soon after he was forced to retire to a monastery.