This paper discusses the process of borrowing of a Cariban number marker *komo by three Tupi-Guarani languages (Wayampi, Emerillon and Zo'é). This process had already been brought to light before (Jensen 1979: 16) and is uncontroversial. In a contact situation prone to borrowings of lexical items, this grammatical marker is apparently the only bound morpheme to have been borrowed by the languages under study. This paper has two main objectives, the first one is to investigate the historical contact situation between the populations involved and the second to describe the specific contact-induced changes at the phonological, distributional, morphological and semantic levels, in order to facilitate hypotheses regarding the socio-historical and linguistic modalities of this loan. The detailed study of the unique case of borrowing of a bound grammatical morpheme in these languages is the starting point for discussing the present understanding of contact-induced changes in general.