This article casts new light on the well-known loss of the masculine genitive plural in Medieval Cypriot Greek and its apparent replacement by the accusative plural. Based on the examination of extensive material from the period, it argues that the phenomenon emerged earlier than so far assumed, i.e. prior to medieval times. Language contact involving mainly Cypriot Greek and Old/Middle French speakers is investigated both from a sociolinguistic and a textual perspective. The findings suggest that language contact with French is likely to have facilitated the diffusion of the construction, but could not have been the initial reason for its emergence. New evidence links the Cypriot phenomenon to earlier occurrences of the same construction found in inscriptions from a wide area, including Egypt, the Middle East and South Russia. Finally, regarding the morphosyntactic origin of the construction, a new explanation is put forward involving functional interplay between the dative, the accusative and the genitive in the late Roman/early Byzantine period, facilitated by phonological overlap in the nominal paradigm.