Recent quantitative work on the variable [g]\~{}[ŋ] alternation in compounds of certain dialects of Japanese has revealed token frequency of the compound as a whole, and of the compound’s second member in its freestanding form, to be important predictors of the alternation. We propose a formal phonological analysis that integrates usage-based factors like frequency with the action of the phonological grammar, extending mechanisms of lexicon–grammar interaction previously proposed in the context of Lexical Conservatism. We demonstrate that our model fits the experimental data better than – or at least comparably to – a theoretically naïve statistical model proposed in previous work. Based on the success of our modelling, we discuss the role of token frequency in phonological patterning more broadly, and how the mechanism that we propose might be extended to unify a range of contradictory frequency-dependent processes that have been observed in the literature.