The movie, which is based on a book of the same name, stars Lily Gladstone, Leonardo DiCaprio, and Robert De Niro (and, boy, do they shine) and tells the chilling true story of how white settlers carried out dozens of murders of members of the Osage Nation in the 1920s. It’s a dark—and essential—tale of American history that I, like KOTFM author David Grann himself, can’t recall learning about in school.

But in Oklahoma, where the murders took place, teachers say they aren’t sure they’re allowed to teach it in class. Under state measure HB 1775, schools are prohibited from teaching the idea that “an individual, by virtue of his or her race or sex, is inherently racist, sexist or oppressive, whether consciously or unconsciously” or that “any individual should feel discomfort, guilt, anguish or any other form of psychological distress on account of his or her race or sex.” (The law is similar to the policies in states like Florida and Texas, among a handful of others, that aim to block the discussion of themes like systemic racism, unconscious bias, and privilege.)

Of course, HB 1775 doesn’t specifically ban Killers of the Flower Moon. But the law is so vague that some educators reportedly say that they have avoided assigning the book and other texts out of fear of punishment.