In A Theory of Justice John Rawls treats the basic structure of society – the way in which political and social institutions work together to assign rights and shape life chances – as the primary subject of political justice. The principles of justice as fairness are selected via the original position behind the veil of ignorance. In the original position parties only know minimal, highly ‘general facts’ about human society, psychology, and politics, including principles of economic theory. Although Rawls very much recognized the significance of the economic dimension for a political theory of justice, by his own admission he said very little about political economy or which economic principles he considered as ‘general facts’. While admitting ‘general facts’ of economic theory looks innocuous, which facts count matters. In the end Rawls permits only market-based regimes – property-owning democracy and liberal socialism – as possible just economic orders. I will argue that this narrowing of the option set does not follow Rawls’ own procedure, admitting order specific assumptions into the original position and across a procedure that is supposed to remain abstract. When these assumptions filter into the original position, justice as fairness becomes a framework for arranging and regulating market-based institutions, rather than a test for a just economic order. I argue that if the original position and four-stage sequence were applied as Rawls originally described – open to institutional form under certain constraints then Rawls’ procedure does not logically entail market-based systems but constrains them. If justice as fairness is to provide more than just conceptual and normative resources for evaluating market-based orders, my critique provides insight for where to begin, and that is with Rawls’ economic assumptions.