UK government’s arms exports to Saudi Arabia during the war in Yemen is high. Exports continued despite evidence that the Saudi-led coalition was violating international humanitarian law (IHL) in Yemen, and despite obligations not to export if there is a risk that the exported equipment can be used in IHL violations. A resulting legal challenge against the UK government provides valuable information about the role of ambiguity in the implementation of arms export controls. Drawing on primary sources from the legal process, it argues that the UK government has taken advantage of linguistic ambiguity.