It’s often difficult for regular investors to get in on the ground floor of hot startups like Pinterest—whose stock rose more than 28% from its initial public offering price of $19, to $24.40 on its first day trading Thursday—as venture capitalists and hedge funds typically dominate private funding rounds. Yet the Pinterest IPO is an exception: One of the social media company’s largest shareholders is Fidelity, which owns Pinterest stock on behalf of many retirement savers, whether they know it or not.

Fidelity owns 7.1% of Pinterest, nearly as much as the 9.6% stake held by Andreessen Horowitz, the famed Silicon Valley VC firm, and more than the 6% owned by Valiant, one of Pinterest’s hedge fund backers. Most of Fidelity’s shares, which are now worth more than $787 million in total, are held in the Fidelity Contrafund, a mutual fund that is a popular offering in 401(k) retirement plans.

Indeed, the massive Contrafund oversees $119.3 billion in assets, of which just under half of 1% is invested in Pinterest. To put that in perspective, the fund has bet more money on Pinterest than it has on other holdings such as Twitter, Coca-Cola and Disney.

And although the IPO values Pinterest just modestly above its valuation in its most recent private funding round, Fidelity still reaped a hefty profit from the public listing. Contrafund, for example, has made a 152% return on its Pinterest investment since it began buying the shares in late 2013, according to securities filings.

A few other Fidelity funds also own smaller amounts of Pinterest stock, including the Fidelity OTC Portfolio, the Fidelity Advisor New Insights fund, and the Fidelity Series Opportunistic Insights fund.

And Pinterest isn’t the only tech IPO the funds are benefiting from this year. Fidelity funds, including all the ones mentioned here, owned shares in Lyft before the ride-hailing company went public in March; their stakes are now worth more than $1 billion combined. They also hold stock in Uber, Lyft’s larger rival that just filed for its own IPO in the coming months, as well as other highly valued private companies such as WeWork and Airbnb.

Fidelity is one of a handful of mutual fund companies that have become more active in startup investing in recent years. Those bets are now beginning to pay off for fund investors: Contrafund, for one, was up nearly 17% year to date through Wednesday—not counting Pinterest’s soaring first day—ahead of the S&P 500’s gain. For those who have a 401(k) plan with Fidelity, there’s a good chance you got a piece of the action too.