Green Day is teasing something.

In a tweet Monday, the punk rockers shared an image of the American Idiot heart grenade surrounded by a nearly whole circle. 

While fans in the comments are hoping that the mysterious post is hinting at new music, it seems to be teasing an announcement for an intimate Lollapalooza aftershow around Green Day’s upcoming headlining set at the Chicago festival.

The same image was also tweeted by Lolla, while the Chicago club Metro tweeted, “Now might be a good time to be signed up for the Metro newsletter…Just sayin.” The Metro logo also features the same almost-circle in Green Day’s post.

Lollapalooza takes place July 28-31, with Green Day scheduled to headline the final day. The lineup also includes Metallica, Machine Gun Kelly, Måneskin, Porno for Pyros, Glass Animals, Turnstile and Wallows.

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