EBay’s stock price rose nearly 10% on Wednesday—one of its largest single-day increases in years—boosting the company’s market cap by about $3 billion to $33 billion.

But the e-commerce company couldn’t credit a stellar earnings report or new product release for the sudden investor appetite; instead it was news of a new partnership with Facebook that did the trick.

Facebook parent Meta announced early on Wednesday that its Facebook Marketplace business will start including some listings from its competitor eBay in the U.S., Germany, and France. For users of Facebook Marketplace, the news means they might stumble upon a product listing from an eBay seller commingled with listings from Facebook Marketplace sellers (to make a purchase from an eBay seller, however, the consumer will still need to leave Facebook and check out on eBay).

“This could benefit people using both platforms,” Facebook parent Meta said in an announcement. “EBay sellers will gain exposure to Facebook’s audience while people using Marketplace will be able to discover a broader array of listings from the eBay community.”

The announcement from Meta came in part as a response to a ruling by the European Commission in November that it would fine Facebook nearly 800 million euros “for breaching EU antitrust rules by tying its online classified ads service Facebook Marketplace to its personal social network Facebook and by imposing unfair trading conditions on other online classified ads service providers.”

While Meta said on Wednesday that it disagrees with the ruling, and continues to appeal the decision, it noted: “We are working quickly and constructively to build a solution which addresses the points raised.” Enter eBay.

For eBay and its sellers, the tie-up provides more visibility for their product listings, though it’s unclear how many listings will make their way to Facebook or how often. EBay told its sellers that the company will decide which listings are shown “based on user interest, shopping trends, and listing quality.” The company could use some help attracting new users as its quarterly active user numbers have largely been flat at between 132 million and 134 million for the past two years. The nearly 30-year-old online auction company is generating $10 billion a year in revenue, though it is growing more slowly than the overall e-commerce market in the U.S.

“We’re always looking for new ways to increase exposure to our sellers’ listings, on and off eBay, as part of our strategy to engage buyers and deepen customer loyalty,” the company said.

EBay added $3 billion in market value in one day—thanks to Facebook’s rival marketplace