GREEN BAY, Wis. (AP) -- Guard T.J. Lang has agreed to a four-year contract extension with the Green Bay Packers.

Lang's agent, Mike McCartney, announced the deal on his Twitter account Monday night and subsequently confirmed it in a text message to The Associated Press.

Lang, a fourth-round pick out of Eastern Michigan in the 2009 NFL draft, became a full-time starter last season and is considered a key cog in one of the NFL's most productive offenses. He started 15 games at left guard and one at right tackle in 2011, after an injury to regular right tackle Bryan Bulaga.

Lang started three games in his first two years in the league.