Defender Tommy Smith has signed a two-year contract extension with Middlesbrough, to run until the end of the 2024-25 season.
The 30-year-old full-back was signed by former boss Chris Wilder on a one-year deal as a free agent last July, following his release by Stoke City.
Smith has gone on to play 27 matches this season, taking his career tally to eight goals in 332 senior appearances.
"He's done fantastically well for us," boss Michael Carrick said.
"He's an important figure for us both on the pitch and in the dressing room."
Smith, who started his career at Manchester City and won promotion to the Premier League with Huddersfield, has been an ever-present in the side since Carrick was appointed in October, following Wilder's exit.