Lewis Page has signed a new deal with Charlton Athletic until June 2020, with an appearance clause that would trigger an extra year at the League One club.
The 22-year-old left-back's existing contract was due to expire at the end of this season, following his move from West Ham United in January 2017.
Page, who was out injured for a year, has now made 27 first-team appearances after returning to action in March.
"Pagey ended the season very well," said Addicks manager Lee Bowyer.
"We definitely missed him in the time he was out. We've probably got the best left-back in the league."
Bowyer's Charlton, who made the League One play-offs in May, are sixth in the table this time around, 10 points off top spot.