Blue-eyed soul crooner Robin Thicke and indie rock hipsters Vampire Weekend are among the nearly two-dozen acts that will headline the Virgin Mobile FreeFest when the free concert returns Sept. 21 to Merriweather Post Pavilion in Columbia, Md., the Washington Post reports.

The bill, which organizer Virgin Mobile USA announced Monday morning, will also include such acts as MGMT and the Avett Brothers.

Thicke’s dance track “Blurred Lines” has been a summer hit.

Tickets to the festival will be available Aug. 9 at noon via Ticketfly; a “pre-sale,” available to Virgin Mobile Facebook fans and previous FreeFest ticketholders (among others), will be Aug. 8.