There is increasing recognition that Indigenous knowledges have considerable potential to enhance collective understandings of and improve responses to complex ecological threats, such as those to cultural heritage from climate change. At the same time, it appears that Indigenous peoples face structural barriers to participation in international organisations that advance knowledge about those problems. Using the conceptual framework of boundary organisations (BOs) theory and case studies of the Intergovernmental Panel on Climate Change (IPCC) and UNESCO, I argue that the lack of meaningful Indigenous engagement in international knowledge institutions is not just an ethical problem; it also undermines the effectiveness of their assessments. The future success of their boundary work partly depends on further engagement with Indigenous stakeholders. At least at the heritage–climate change nexus, the salience, legitimacy, and credibility of IPCC and UNESCO assessments require substantive Indigenous representation alongside other state/non-state parties. Successful experiences in biodiversity governance indicate that incorporating the principles of the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) would enhance Indigenous engagement in UNESCO and the IPCC.