The Colts are reportedly closing in a deal to keep left tackle Anthony Castonzo in Indianapolis long-terms.

According to NFL Media's Ian Rapoport, the Colts and Castonzo are finalizing a four-year extension, worth $42 million. The deal is expected to average $10.5 million per season.

The Colts' first-round draft choice in 2011, Castonzo was entering the final season of his rookie contract. The 6-foot-7, 311-pound Castonzo has started every game for the Colts the past three seasons.

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The move to lock up Castonzo comes after the team agreed to an extension last month with another impending free agent, wide receiver T.Y. Hilton.

More work remains, though, for general manager Ryan Grigson, as Colts tight ends Coby Fleener and Dwayne Allen are also entering the final years of their contracts. The team will also need to hand out what should be one of the NFL's richest contracts to quarterback Andrew Luck, perhaps as early as next offseason.

(h/t Twitter)