Washington State Governor Jay Inslee calls it a “serious error,” “unacceptable” and “maddening.”

Approximately 3,200 inmates in Washington’s prison system have been released early from their sentences due to a “sentencing computation issue” at the Department of Corrections, according to the governor’s office. That error has miscalculated the sentences of prisoners, letting them out early for nearly 13 years.

“These were serious errors with serious implications. When I learned of this I ordered DOC to fix this, fix it fast, and fix it right,” Inslee said in a statement.

“I have a lot of questions about how and why this happened, and I understand that members of the public will have those same questions,” he said. “I expect the external investigation will bring the transparency and accountability we need to make sure this issue is resolved.”

In 2002, Washington state implemented a new sentencing system for some prisoners at the order of the Supreme Court. That system has been miscalculating sentences ever since and has been releasing prisoners about two months early.

Inslee’s office said that the prisoners that have been let out of jail early are a narrow subset of the prison population, about 3 percent.

Inslee has ordered that releases be halted until hand calculations can be done to determine the proper release date. Offenders that were released early over the years are being contacted to fulfill their remaining time. They will either be placed in a work-release program or be sent back to prison.

A software fix to the department of corrections is expected by Jan. 7, 2016.