The Dolphins have agreed to terms with one of their most productive players.

Restricted free agent linebacker Kiko Alonso and the team have agreed to a four-year contract worth $28.8 million, according to Armando Salguero of the Miami Herald.

NFL Network’s Mike Garafolo reports Alonso’s deal is officially a $25 million three-year extension on his extant one-year tender agreement, including $18.5 million in guarantees, in addition to the $3.9 million he received as part of his tender.

The agreement keeps Alonso in Miami through 2020.

Alonso joined the team last offseason in a trade with Philadelphia that also included cornerback Byron Maxwell, and went on to lead Miami with 115 combined tackles.

Miami said that retaining existing players was to be their primary concern this offseason, a promise they have lived up to, while also making a number of prominent deals with players from other teams, including free agent linebacker Lawrence Timmons.

The move represents one of their most pronounced attempts to fortify their defensive core, having already signed defensive ends Cameron Wake, Andre Branch, and William Hayes, Timmons, and safety Reshad Jones.

Despite these additions, the Dolphins are expected to still address their defense in the NFL Draft next month.

UPDATE (4:27 pm EST): The Dolphins announce Kiko Alonso’s contract extension

Miami picks at No. 22 overall.