The stock purchase adds to the almost 170 million shares that Berkshire Hathaway already owns and would see it overtake State Street Corp. (STT) to become Apple’s third-largest investor, according to data compiled by Bloomberg (BLOOMBERG). The Cupertino, California-based company was already Buffett’s biggest shareholding.

Buffett’s announcement comes just days after Apple reported quarterly sales and profit that topped analyst estimates on surging services as revenue rose at the fastest pace in more than two years. The results helped end a recent swoon in Apple shares amid concern its flagship iPhone X model was struggling to win consumers.

“It is an unbelievable company,” Buffett said, according to CNBC. “If you look at Apple, I think it earns almost twice as much as the second most profitable company in the United States.”

Berkshire Hathaway is holding its annual meeting this week in Omaha, Nebraska.

While Apple still gets more than 60% of its revenue from iPhones, services are playing an increasingly important role as growth in the overall smartphone market slows.

For more about Apple’s other services, watch Fortune’s video:

Chief Executive Officer Tim Cook sells a growing array of services through a base of more than 1.3 billion Apple devices, including music, cloud storage, movies and apps. Revenue from services surged 31 percent to a record $9.2 billion in the most recent quarter.

An Apple Music subscription costs $10 per month (unless they’re on a family plan), and the number of paying users recently hit 40 million. The middle tier for iCloud storage costs $2.99 a month. The company now has 270 million paid subscribers across applications and its own services, up by 100 million from the same period a year ago.