While much interdisciplinarity brings together proximate fields, broad interdisciplinarity sees integration between disciplines that are perceived to be non-neighboring. This paper argues that the heterogeneity among disciplines in broad interdisciplinarity calls for stricter epistemic norms of testimony for experts that act as translators between the disciplines than those suggested for intra-scientific testimony. The paper is structured around two case studies: the affective turn in social theorizing and the use of quantum mechanics in critical theory as exemplified by Vicky Kirby’s use of work by Karen Barad. These are argued to be instances of broad interdisciplinary borrowing where few translators have joint expertise in both disciplines. For most, therefore, the engagement with for instance the integration between quantum mechanics and critical theory is possible only by the aid of translators. For those without sufficient interactional expertise, however, the epistemic credentials of the translations they inevitably rely upon are inscrutable. Furthermore, any comparison between translations is challenged since translations are argued to be few due to the cognitive divergence between disciplines in broad interdisciplinarity. Consequently, the epistemic integrity of broad interdisciplinarity can only be secured through additional norms of testimony for translators. The paper proposes that (a) all translator’s testimony in broad interdisciplinarity must aim to be neutral with respect to disputed issues within the relevant disciplines and (b) any deviation from (a) must be clearly highlighted.