Hot on the heels of a Virginia brewery's cereal-inspired marshmallow beer, another way for grown adults to feel like kids again has emerged. Marshmallow-only Lucky Charms are back—this time with unicorn and rainbow shapes. Unfortunately, only 15,000 boxes of the sweet stuff are up for grabs.

If you were already planning on treating yourself by picking up some regular Lucky Charms from your local supermarket, be on the lookout for promotional boxes that say “You could win a box of only marshmallows” on the front. The inside panels of those boxes contain codes that can be entered at MarshmallowOnly.com for your chance to win one of the rare pure-marshmallow boxes. The promotion will run through the summer, so you’ll have plenty of time to enter up to 30 codes. Here's a list of participating retailers carrying the coded boxes [PDF].

This isn’t the first time that General Mills, the maker of Lucky Charms, has held this sweepstakes. In 2015, the company gave away 10 boxes of marshmallow-only cereal (or, as it calls the sugary shapes, “marbits”). Based on the popularity of that promotion, it handed out 10,000 boxes in 2017.

"It's no secret that Lucky Charms fans love the marshmallows," Scott Baldwin, director of marketing for cereal at General Mills, said in a statement. "Consumers have flooded our inboxes and swept our social feeds begging for Lucky Charms Marshmallow Only to return. You asked, and we listened!"

If you’re not feeling especially lucky, you can buy similar versions of the marshmallows on Amazon. Retailers like Medley Hills Farm and Hoosier Hill Farm (which are apparently unrelated companies) sell one-pound bags of cereal marshmallows for $11 and $10, respectively. You can also order an 8-pound bag, or, if you’re feeling especially peckish, a 40-pound case of dehydrated marshmallows for $228. As one Amazon reviewer wrote, it's “just the right amount."