The Council of Europe Convention on preventing and combating violence against women and domestic violence (Istanbul Convention) is only the second international human rights treaty that the EU has signed. The process of its signature by the EU and the Member States has been fraught with policy and legal tensions. This article examines Opinion 1/19 in which the Court of Justice dealt with legal basis and procedural issues that are central to the functioning of mixed agreements. The analysis teases out the themes of procedural integrity and pragmatism that emerge, reflects on the reticence of the Court to deal with certain issues, and explores the implications of the Opinion for our understanding of mixed agreements in the EU legal order.