Miranda Fricker defines epistemic injustice as harm to someone specifically in their capacity as a knower. In her book on the topic, she focuses primarily on testimonial injustice, which harms a potential informant. When you are the victim of testimonial injustice, you know (or are at least in a good enough position to know, given the issue), but your word is not taken as seriously as it should be. She also discusses, at less length, hermeneutic injustice, which occurs when someone has a kind of knowledge implicitly but — for unfair reasons — lacks the conceptual resources to articulate that knowledge. (Witness the need to name evils like sexual harassment and marital rape.)
Understandably, Fricker focuses on epistemic injustices perpetrated against the oppressed. She pays much less attention to epistemic injustices that more typically accrue to the powerful. I dub one such form of epistemic injustice negative epistemic injustice. The motivating thought here is that people have an epistemic right not only to be listened to when they are or might be right; they also have an epistemic right to be told when they are or might be wrong. Whereas the relatively powerless are more likely to experience positive epistemic injustice (being told that they are wrong or being assumed to be wrong when they’re not), the powerful are more likely to experience negative epistemic injustice (being told that they are right or being assumed to be right when they’re not).
It’s hardly an insight that the powerful are often surrounded by yes-men, that the emperor is the last to find out that he’s naked because no one is willing to disabuse him of his mistake. The insight here — if there is one — is that this is an obvious form of epistemic injustice.
(I recently stumbled across this idea while fuming about the fact that Joshua Greene, a highly-regarded neuroscientist at Harvard, remains ignorant of the fact that Phineas Gage did not become, for all anyone knows, a sociopathic drifter after his head was punctured by a railroad spike in a freak accident.)