This article critiques the articulation of the legal framework applicable to Australian Defence Force operations in Afghanistan found in the Inspector-General of the Australian Defence Force Afghanistan Inquiry Report (Brereton Report). In particular, using the Australian experience in Afghanistan as a case study, the article argues, on the basis of the rules of treaty interpretation, that where a foreign State party to Additional Protocol II (AP II) intervenes in a non-international armed conflict (NIAC) to which AP II applies, that foreign State is bound by AP II, in addition to the host State and non-State armed actors that are parties to the NIAC. The article concludes by outlining the reasons why the Brereton Report's silence in relation to AP II matters.