The basic characteristic of composite codeswitching is that the languages involved share responsibility for framing bilingual constituents. This paper points to evidence of this characteristic in the nature of morpheme distribution in mixed possessive constructions in Ewe–English codeswitching, spoken in Ghana. An Ewe semantic distinction between two types of possessive constructions is consistently neutralized when English possessum nominals are used instead of their Ewe counterparts, and the paper demonstrates that the neutralization of this distinction results from direct mapping of English-origin grammatical information about English nominals onto Ewe grammar. It explains that this mapping of information from one grammar onto another one is characteristic of composite codeswitching and that it is facilitated by the fact that language production is modular in the sense of Levelt ((1989). Speaking: From intention to articulation. Cambridge, MA: MIT Press) and Myers-Scotton ((1993). Duelling languages: Grammatical structure in codeswitching. Oxford, UK: Clarendon Press; (2002). Contact linguistics: Bilingual encounters and grammatical outcomes. Oxford, UK: Oxford University Press).