Abstract The motet Huc me sydereo by Josquin des Prez appears in both five- and six-voice versions, having led scholars to debate which version is authentic to the composer’s original conception. The authoritative New Josquin Edition presents the motet in its six-voice version; in the critical commentary, editor Bonnie Blackburn defended it as Josquin’s original. More recently, Joshua Rifkin has demonstrated on stylistic and source-critical grounds that the five-voice version was original, with a sixth voice having been added later. In this article, I present new findings on the manuscript St Gallen 464, an important early source for Huc me sydereo, which reinforce arguments defending the authenticity of the five-voice version. I show that the origin of the sixth voice can be isolated to a trio of sources produced on the Italian peninsula in the 1510s, all but eliminating Josquin as a candidate as its author. Moreover, through a new identification of the original scribe and owner of St Gallen 464, I shed new light on that manuscript’s date and provenance. In so doing, I demonstrate how the study of musical sources and transmission can carry direct importance for essential performance decisions.