The NI Prison Service has made changes to its policy on which books are allowed into its prisons.
The director general ordered a review after it emerged that inmates at Maghaberry Prison were unable to access a book on dissident republicanism.
Ronnie Armour met the book's author, the academic Dr Marisa McGlinchey, to brief her on the new guidelines.
Until this case arose, no books relating to terrorism or paramilitaries were allowed into the jail.
The review found this policy was "not proportionate".
From now on, books will be allowed into the prison "unless they breach specific guidelines which include the promotion of, or support for terrorism/paramilitaries, or overtly promote or encourage the commission of criminal acts".
If there are concerns about a particular book, these will be reviewed by a deputy governor, and if a ban is upheld, there will be an appeals procedure.
The Northern Ireland Prison Service said this was "an in-depth review, which had prompted serious discussions" in the service.
It accepted that the blanket ban was not appropriate, adding that it was a "changing organisation and learning organisation".
Constructive and genuine
Dr McGlinchey said Mr Armour had explained to her that the blanket ban on any books about terrorism or paramilitaries had been introduced because the prison service wished to have a neutral environment.
The director general stressed that prison officers were still living with the impact of the Troubles and "ongoing violence", citing the murders of David Black in 2012 and Adrian Ismay in 2016, both by the New IRA.
Dr McGlinchey said she was pleased with the outcome, describing her meeting with Mr Armour as constructive and genuine.
"It was clear that the matter had been taken very seriously," she said.
The Department of Justice said new operating procedures had been put in place following a review into arrangements for providing prisoners with books.
"Books and other reading material will now be permitted unless they overtly promote or encourage the commissioning of criminal acts or otherwise break the law," the department told BBC News NI.
"Decisions will be taken on behalf of the governor of each prison, with a review process available at headquarters."