Appearing at the Los Angeles premiere of her new indie comedy-drama Perks of Being a Wallflower, the 22-year-old actress floated down the red carpet looking a picture in a backless lace dress.
Unfortunately, a pesky see-through pastie barely covering her left nipple made a surprise cameo see above. Talk about the "perks" of being a wallflower!
Luckily Emma spotted the side-boob calamity and adjusted her outfit accordingly.
The near-nip slip didn't faze the elegant Harry Potter star, who generously chatted with fans and signed autographs.
Emma took to Twitter a few hours ago to respond to the news that she is "the most dangerous celebrity" on the web, with nearly one in eight searches containing her name leading to malicious websites.
"Apparently I'm 'dangerous!'" she wrote.
"I can't do anything to stop these people so please take care and only go to official sources."