ABSTRACT This paper offers an account of institutional testimonial justice and describes one way that it breaks down, which we call institutional opacity. An institution is opaque when it becomes resistant to epistemic evaluation and understanding by its agents and users. When one cannot understand the inner workings of an institution, it becomes difficult to know how to comport oneself testimonially. We offer an account of an institutional ethos to explain what it means for an institution to be testimonially just; (...) we then describe how an ethos of institutional testimonial justice can break down when the institution becomes opaque. An opaque institution is especially problematic for individuals and groups already rendered epistemically vulnerable during their interactions with that institution, which we call epistemically vulnerabilised individuals. We articulate the features of an encounter between an epistemically vulnerabilised individual and an opaque institution. We end by tracing ameliorative strategies that could help repair a deteriorated institutional ethos of testimonial justice. (shrink)