The Pirates recalled Mattson from Triple-A Indianapolis on Saturday, Danny Demilio of PittsburghBaseballNow.com reports.
Mattson will rejoin the Pirates' bullpen after posting a 1.86 ERA and 1.45 WHIP with 11 strikeouts in 9.2 innings since being optioned to Triple-A on May 20. Antwone Kelly was optioned to Indianapolis in a corresponding move.