This article supports calls for an increased integration of patients into taxonomic decision making in psychiatry by arguing that their exclusion constitutes a special kind of epistemic injustice: preemptive testimonial injustice, which precludes the opportunity for testimony due to a wrongly presumed irrelevance or lack of expertise. Here, this presumption is misguided for two reasons: (1) the role of values in psychiatric classification and (2) the potential function of first-person knowledge as a corrective means against implicitly value-laden, inaccurate, or incomplete diagnostic criteria sets. This kind of epistemic injustice leads to preventable epistemic losses in psychiatric classification, diagnosis, and treatment.