Since the turn of the century, the fight against marriages of convenience (or “sham marriages”) has become a key part of European migratory policies. In Belgium, the government has established a procedure aimed at evaluating “mixed” marriages between Belgian citizens and nationals of non-EU countries in order to detect – and prevent – marriages of convenience, that is marriages undertaken with the sole objective of obtaining a residency permit. Through analysis of a number of legal and policy documents from both Belgium and the European Union, this article aims to explore the discursive aspects of the legal-administrative definition of a “marriage of convenience” in these procedures. We first show how this definition constitutes the product of a process of discursive construction and explore how it is shaped and codified in the different texts and practices that make up the enquiries. We then explore how this process leaves open the door to discrimination – and notably gendered discrimination – as well as instances of moral gatekeeping.