Mary Astell is a fascinating seventeenth‐century figure whose work admits of many interpretations. One feature of her work that has received little attention is her focus on bad custom. This is surprising; Astell clearly regards bad custom as exerting a kind of epistemic power over agents, particularly women, in a way that limits their intellectual capacities. This article aims to link two contemporary sociopolitical/social‐epistemological projects by showing how a seventeenth‐century thinker anticipated these projects. Astell's account of bad custom shows that (...) she was attuned to the kinds of institutional or structural explanations theorized by Sally Haslanger, and that she acknowledges that bad custom—as an institutional or structural explanation—is intimately linked with epistemic injustice, albeit a kind not yet captured by contemporary social epistemologists. I call this form of epistemic injustice found in Astell epistemic internalization injustice. I argue that the epistemic significance of Astell's notion of bad custom is that it enables us to understand how bad custom conditions human relations in such a way as to result in epistemic injustice. Through coming to understand her notion of bad custom, we can expand our understanding of social epistemic phenomena like epistemic injustice. (shrink)