The article explores how the European Court of Justice (ECJ) has instrumentalized international law in order to secure its constitutional agenda. It argues that the mediation of internal and external orders has been dominated by a constitutional logic. The fact that international integration is depended on domestic dynamics is not new. However, the EU shows is that the openness to an international legal scenario relies on the ‘constitutional surplus’ that is generated either by the inclusion or the exclusion of international law. In order to assess this interest–based internationalization, the paper deals with the principle of consistent interpretation (PCI). It shows how the PCI provides the malleability necessary to articulate the openness (or closure) of the EU legal system without having to deal with the formal repercussions of direct effect. The article explores the challenges that such loose application presents for the EU quasi-federal scheme.