International treaties create a layer of law that is particularly hard to change: While modern treaties entail significant constraints on domestic law-making, amendments require a new consensus of state parties. This creates a conflict with a core aspect of democratic constitutions: the power of new majorities to revise the laws made by their predecessors. In particular, several obligations of international economic law, namely regulatory stability promises in investment protection treaties, but also criminalization requirements under the UN drug control conventions face critique for overly diminishing domestic policy space. How can democratic constitutions deal with those tensions? One approach that is common in some countries accepts a power to legislate in violation of treaty obligations. But denying treaties the quality as real law in the domestic sphere risks to undermine the benefits of the instrument without truly solving the democracy concerns. Instead, democratic constitutions can be read to entail certain standards for engaging in treaties, namely (i) procedure-related duties to include denunciation clauses and political reform mechanisms in the treaty, and (ii) the need to establish a substantive justification for treaty constraints on future domestic law-making by legitimate aims of international constitutionalism or co-operation.