Did you know you can buy diamond rings at Costco? And expensive ones, at that.

The warehouse retailer said during its latest quarter ended May 12 it got a sales boost thanks to a customer purchasing one of its rings for more than $400,000. It didn't say which ring, exactly, but a search on Costco's website reveals only one ring priced in the $400,000 range: A "Round Brilliant 10.03 carat VS1 Clarity, I Color Diamond Platinum Solitaire Ring." Costco's website shows 500 different rings for sale, many costing more than $50,000.

Costco said same-store sales were up 5.6% in the latest quarter, excluding any effects from gasoline prices and currency fluctuations. That was better than the 5.48% growth analysts were expecting, based on Refinitiv data.

Total revenue rose 7.4% to $34.74 billion, topping estimates for $34.71 billion.

But Costco shares were falling about 2% Friday morning, despite the upbeat earnings report, as investors fear the impact additional tariffs might have on its business.

"At the end of the day, prices will go up on things," CFO Richard Galanti told analysts on a post-earnings conference call. "We want to be the last to raise them. And when prices are going down, we want to be the first to lower them."

While people may associate Costco with selling things like bundles of toilet paper and giant boxes of cereal in bulk, its members also have access to other services to book vacations and buy cars. Many shoppers enjoy the treasure hunt experience Costco's stores offer, as eagle-eyed shoppers can often spot miscellaneous items there, which is one way the retailer makes it worth shoppers' while to trek to stores.

In selling diamond jewelry, Costco has promoted its wedding business for several years. Brides on a budget can buy everything from flowers to sheet cakes and invitations there.

Costco declined to comment any further on the ring sale.