This paper argues that the strong conception of popular sovereignty employed in the German Federal Constitutional Court's recent decision on the Treaty of Lisbon is incoherent and should not be used as the centerpiece of a democratic constitutional theory. Strong conceptions of popular sovereignty are usually defended on the basis of the claim that an appeal to strong popular sovereignty is necessary to ground the legitimacy of constitutional law. In fact, strong conceptions of popular sovereignty eliminate the conceptual space for the idea of legitimate law. This thesis is developed through a critical discussion of Carl Schmitt's constitutional theory-which appears to be the main inspiration behind contemporary arguments for strong popular sovereignty-as well as through an analysis of the Lisbon decision of the Bundesverfassungsgericht.