After beginning the 2017 season back in Fresno, Jankowski was called up to the majors for the first time on May 22, 2017.[2] He made his MLB debut for the Astros on May 24 against the Detroit Tigers, allowing two runs in one inning of work. In his second appearance, on May 29 against the Minnesota Twins, Jankowski allowed four runs in 2 1⁄3 innings but was credited with his first win. On August 2, he made a third appearance, pitching a scoreless inning against the Tampa Bay Rays.[3]
Los Angeles Dodgers
On August 20, 2017, Jankowski was claimed off waivers by the Los Angeles Dodgers.[4] He was designated for assignment on September 2 after just a few games with the Triple-A Oklahoma City Dodgers.[5] Jankowski was released by the Dodgers prior to the 2018 season.[6]
Los Angeles Angels
On April 9, 2018, Jankowski signed a minor league contract with the Los Angeles Angels.[7] He was released on May 25.
Steel City Slammin' Sammies
In 2020, Jankowski signed with the Steel City Slammin' Sammies of the Washington League. In 3 games for the team, he struggled to an 0-1 record and 6.75 ERA with 4 strikeouts, 6 walks, and a saves.