The Russian invasion of Ukraine has widely been seen as a failure of the international legal order, which could neither stop Russia from launching a war of aggression, nor prevent the perpetration of international crimes. In such a reading, great power politics have (once again) trumped international law. We argue instead that international law plays a crucial part in the conflict by providing a semantic infrastructure, which the opposing parties use to justify their actions, try to re-draw limits of permissible action and negotiate changing ‘red lines’ with the enemy. Drawing on the notion of lawfare, we show how the pragmatic (mis-)use of international law flexibly delineates boundaries and stabilizes expectations between adversaries even as they are contested in the current war. We focus on claims about self-determination and self-defence to justify the use of force; categorizations of combatants; and weapons transfers and the status of third states. That international law can be violated or reinterpreted to breaking point does not make it irrelevant. To the contrary, it recalls its important role as a language of conflict and compromise, beyond strictly legalist as well as dismissive realist views.