Methodological nationalism assumes that, to understand a phenomenon, nation- states are the relevant units of analysis. This assumption has been recognized as a source of bias in most of the social sciences. Does it bias Rawls' understanding of justice, too? This paper argues that it does for at least two reasons. Firstly, what Rawls thinks justice requires on a global scale falls short of what states and international organisations actually do. Secondly, framing the difference principle in national terms, as Rawls did, is a way to increase the “citizenship rent”, or the revenue a person receives just by being citizen of a rich country The paper argues that methodological nationalism biases Rawls’ understanding of justice by affecting both the plausibility and the coherence of his theory.