Gonzalez was optioned to Triple-A prior to the All-Star break to stay on track and to allow the O's to add another person to the roster during that time. He is coming off back-to-back eight-inning outings.
Guilmet, 26, has posted a 5.23 ERA and 12 strikeouts in 10 appearances for the Orioles this season.
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Facebook and Twitter @britt_ghiroli. This story was not subject to the approval of Major League Baseball or its clubs.