Much discussion of the ethics of war revolves around civilians' alleged special claim to protection, expressed in the principle of non-combatant immunity. This article shows that its supporters do not give persuasive reasons for why civilians should be protected from deliberate harm ahead of combatants. The principle moreover problematically relies on the significance of intention. Intriguingly, the principle is defended in the face of recognising these issues. Its defenders argue that the principle must be maintained because without it we would be unable to distinguish legitimate uses of political violence from mass murder and terrorism. This article argues instead that the principle's role in making permissible political violence classified as ‘war’ must be considered: it works to enable what it seeks to prevent, namely making the killing of civilians acceptable.