The National were among the headliners performing at Eaux a Claire Festival, organized and curated by Justin Vernon (Bon Iver). Vernon made a guest appearance with the National, as did Sufjan Stevens, but perhaps the biggest surprise of the performance, for those in attendance, was a slowed down cover of “Peggy-O”, as interpreted by the Grateful Dead.

As Stereogum reports, the Grateful Dead cover was something of a “curveball,” but the band certainly injected their own energy and passion into the classic tune. For fans of the band or the Dead, this should come as no surprise, as the National have been working on a Grateful Dead tribute album, and were even featured in the recent Bob Weir documentary, The Other One: The Long, Strange Trip of Bob Weir.

We’ll be sure to update once video of the cover surfaces.