As a little preview of their upcoming stadium tour that starts in a week, Rihanna joined Eminem on stage during his headlining set at Lollapalooza. The frequent collaborators performed “Monster” and “Love The Way You Lie” and, more surprisingly, Rihanna provided vocals on Eminem’s “Stan” from 1999’s The Marshall Mathers LP. Watch video from the show below.

Eminem and Rihanna’s joint tour begins 8/7 in Los Angeles.