“SLAVERY BY Another Name,” a book by Wall Street Journal senior correspondent Douglas A. Blackmon, won a 2009 Pulitzer Prize for its historical account of the exploitation of African American prisoners in Southern states from the late 19th century until World War II. But the state of Alabama seems to regard the book as not so much a great work of nonfiction as a potential security threat.

Officials with the Alabama Department of Corrections barred Mark Melvin, an inmate in its Kilby Correctional Facility, from acquiring the book. They cited Paragraph (V)(G)(4)(a) of Alabama Department of Corrections Regulation Number 448, which states that a piece of incoming mail or other material “may be determined to be a threat to the security of the institution” if it could “reasonably be considered” to be “an attempt to incite violence based on race, religion, sex, creed or nationality.”

Mr. Melvin, through his lawyers at Alabama’s Equal Justice Initiative, sued corrections officials last month in federal court, claiming the officials engaged in “censorship” in violation of his First Amendment rights. “Defendants’ decision to ban the book was based on their desire to restrict access to information about historical racism in the Southern United States and is not reasonably related to a legitimate penological purpose,” the complaints asserted.

Mr. Melvin, who is white, is serving a life sentence for his role in a murder committed when he was 14; he is now 33. He has worked in the prison library and, according to his lawyer Bryan Stevenson, reads up to five books each month. Mr. Stevenson procured the book for Mr. Melvin.

Prison officials must have substantial flexibility to maintain order. Inappropriate or incendiary material should be banned, whether it relays bomb-making instructions or promotes violence between racial groups. “Slavery by Another Name” does not qualify as either. It is instead a meticulous work that memorializes a post-Civil War period in American history when African American men were arrested — sometimes on trumped-up charges — and forced to work for wealthy locals. It is not hard to see how reading about the injustices of this deeply regrettable era could stir up emotions, but there is no reason to believe that it will incite violence. If “Slavery by Another Name” is off-limits, is there anything prison officials could not bar?

Rather than banning the reading of such books, prison officials should be celebrating the fact that inmates endeavor to better themselves from reading this type of quality material. Mr. Melvin, for example, may one day find himself back in the community at large. The more educated he is, the better chance he will have to live a productive and law-abiding life.