Oxford have confirmed the signing of defender Charlie Raglan on a two-year deal following his loan spell from Chesterfield.
The 24-year-old made 17 starts for United last season and was released by Chesterfield following their relegation to Sky Bet League Two.
Raglan has the option for a further year and is relishing another opportunity at the Kassam Stadium.
"The manager and staff are great and I want to replay the faith they have shown in me by being part of a successful side next time around," Raglan said on Oxford's official website.
"The club is always looking to push on and move forward and that is exciting to be involved in."
Oxford boss Michael Appleton feels the best is yet to come from Raglan.
"Charlie is still only 24 and we feel will continue to progress. He is already a very good defender who is comfortable on the ball and he showed a fantastic attitude last season," Appleton said.
"He knows we are looking to further strengthen in that area and is up for the challenge, so we look forward to working with him again."