This article examines how European Union (EU) arms control measures are tailored to its constitutional foundations. EU Member States subject shipments of arms and components to controls so as to screen them for risks and potentially block them. In this context different Member States may make different geopolitical and humanitarian risk assessments. Existing EU measures have achieved only limited security screening harmonisation, and have left room for Member States to shirk their obligations under international humanitarian law. But in case of joint arms production, which the EU subsidises to become more autonomous, one Member State’s arms controls may block another State’s exports and thereby jeopardise cooperation. This article posits that any reform of EU arms controls should start by re-evaluating their present legal basis. A constitutional competence analysis shows that controls on arms shipments to non-EU states should be regulated in part through the Common Commercial Policy (CCP), and not just through the Common Foreign and Security Policy (CFSP). This would be consistent with other EU regulatory regimes for trade security. While a joint CFSP-CCP approach cannot fully prevent conflict, since this would require further foreign policy harmonisation, it could help foster security convergence and strengthen humanitarian due diligence mechanisms.