The Rangers selected Ahlstrom's contract from Triple-A Round Rock on Monday, Jeff Wilson of AllDLLS.com reports.
Ahlstrom earned the promotion by putting up a 2.76 ERA and 33:8 K:BB over 29.1 innings with Round Rock. The left-hander will turn 27 later this month and will be making his major-league debut when/if he gets into a game.