Solomon was recalled from Triple-A Sugar Land on Thursday, Danielle Lerner of the Houston Chronicle reports.
Solomon tossed two scoreless innings for the Astros earlier in the season, but he was sent down at the end of April and made nine appearances (six starts) with the Triple-A club. He posted a 6.11 ERA and 1.51 WHIP in 35.1 innings during that time, but he'll now rejoin the big-league bullpen after left-hander Ryan Hartman was sent down Thursday.