This paper aims to contribute to the literature on ‘institutional maintenance work’. Focusing on the institutional disruption resulting from a regulatory project of market rationalization, it enriches the description and analysis of the specific institutional maintenance work performed by powerful actors who engage in resistance against what they perceive as a threat to their discretion. Built on an in-depth qualitative study, our case concerns an attempt to change the form of over-the-counter markets as part of a recent financial reform. The paper contributes to the expanding literature on the maintenance of institutions by suggesting, in particular, that the creation of incommensurables should be added to the list of strategies available to powerful incumbents seeking to resist institutional change. Bridging the gap between the literatures on institutional maintenance and commensuration, it also demonstrates that specific institutional changes can usefully be understood as changes in commensuration systems. This innovatively suggests the existence of degrees of commensuration and calls for a finer-grained understanding of the institutional work required to maintain institutions in a context where the degree of commensuration experienced by a field or a market threatens to increase under coercive pressure.