This paper investigates the grammar and usage of one in Singapore English, which exhibits the influence of both Chinese and English, the two dominant languages in the multilingual ecology of Singapore English, as well as the influence of relevant linguistic universals. The grammar of one is essentially the grammar of Chinese de filtered through the morphosyntax of English one. The corpus data show that some one forms which are judged acceptable by native-speaker informants have nevertheless low frequency of use. It is argued that usage plays an important role in the success of contact-induced grammatical innovation, and propose an exemplar-based model of relexification that provides a satisfactory explanation of the grammatical properties and usage patterns of one in Singapore English.