DALLAS (AP) — A medical school and research center in Texas must repay $13 million to the U.S. government for violating certain rules related to use of federal research grants.

The University of North Texas Health Science Center agreed to the repayment, announced Friday. A statement from U.S. Attorney Erin Nealy Cox says the case involved allegations that center officials inaccurately measured, tracked and paid researchers related to some National Institutes of Health grants.

Center officials self-disclosed the errors, in a review from 2011 through February 2016, and cooperated in the investigation. UNT has since upgraded compliance monitoring and procedures.

The University of North Texas System includes the University of North Texas in Denton, the University of North Texas Health Science Center in Fort Worth and the University of North Texas at Dallas.