The aim of this paper is threefold. First, it provides a description of the morphological and syntactic properties of comitative adverbs in Japhug and other Gyalrong languages, a class of adverbs derived from nouns by a combination of prefixation and reduplication. Second, it argues that they result from a two-step derivation, first from noun into proprietive denominal verb, then from that verb into a participial form. The resulting form is later reanalyzed as a single morphological derivation from the noun. Third, this paper contributes to the study of language contact within the Gyalrongic group by showing how one of the two processes for building comitative adverbs in Japhug is borrowed from the neighbouring Tshobdun language.