Modern understanding of the production and dissemination of thirteenth-century polyphony is constrained by the paucity of manuscript sources that have been preserved in their entirety; the panorama of sources of medieval polyphony is essentially fragmentary. Some of the surviving fragments, however, were torn from lost books of polyphony that were to some extent comparable to well-known extant codices. The fragment of polyphony preserved in the binding of manuscript 6528 of the Biblioteca Nacional de Madrid is illustrative in this respect. This fragment displays a number of codicological and musical features that are strikingly similar to those of the Florence manuscript (F). Both sources share format and mise-en-page, make use of similar styles of script, notation and pen-work decoration, transmit the pieces in the same order, and present virtually identical musical readings. The Madrid fragment thus provides new evidence for a standardised production of polyphonic books in thirteenth-century Paris. The study provides a detailed account of the fragment’s codicological and philological features, and explores the hypothesis that it originated in the same Parisian workshop that produced F.