On Monday, Buffett told CNBC his insurance and investing conglomerate had bought 72 million of Apple’s shares in the first month of January alone. He also owned up to the fact that Apple (AAPL) is one of the legendary investor’s own stock picks, and not one chosen by his lieutenants.

“Because I like it,” Buffett said on CNBC in response to why Berkshire had bought so much of iPhone maker’s stock. “Apple strikes me as having quite a sticky product.”

Over the weekend, Buffett released his annual letter to shareholders in which he berated Wall Street money managers for charging high fees and producing lousy investment results. He also offered a rebuke to Donald Trump, saying immigrants are what has made America great.

Berkshire started buying shares of Apple in mid-2016, and had 61 million shares by the end of the year. Buffett said Berkshire’s Apple stake is now more than double that, and worth about $17 billion and amounts to 133 million shares. Buffett bought his most recent stake between Jan. 1 and Jan. 31—the day Apple reported that its sales rose $2.5 billion, or 3%, in the last three months of 2016, which was higher than expected.

Buffett says he hasn’t bought any shares in Apple since the earnings announcement, but he didn’t give any indication that his enthusiasm for the company or its stock had waned. What’s more, Buffett said Apple Chief Executive Tim Cook has done a “terrific job.” Buffett’s investment in Apple now amounts to about 2.5% of the company. That makes Buffett, who for most of his career has shunned tech stocks, Apple’s fifth largest outside investor, and probably its most active. Vanguard and Blackrock, for instance, Apple’s No. 1 and No. 2 largest outside investors, mostly own the stock because of their index funds.

Overall, Buffett told the television network, Berkshire has spent about $20 billion on stocks since just before the U.S. election in November, adding that he thinks the U.S. market is cheap with interest rates at current levels. “I’ve bought a lot of stock in the last four months,” Buffett said. Nonetheless, he said it was extremely hard to time the market and that stocks could plunge tomorrow. “[The market] could go down 20% tomorrow, but I’ll still be happy because I have been buying good businesses.”

Buffett said that Berkshire’s positions in airlines remains unchanged. He said pricing shares of airlines has historically been a “very tough game” and that he has not met the chief executives of any of the four airlines in which Berkshire holds stakes.

Investors in Apple seemed to react with caution to Buffett’s announcement that he bought a massive new quantity of shares. Perhaps because Buffett’s buying was even bigger than expected, shares of Apple are up 22% in the past three months. Some observers had seen that movement as a sign that investors in general were regaining their optimism about Apple’s prospects, after rising skepticism that the iPhone maker would be able to continue its past success. Indeed, my colleague Shawn Tully has argued that the company’s lack of diversity—more than 70% of its sales come from the iPhone—and the fact that Apple is already dominant in the smart-phone market make it nearly impossible for Apple to live up to investors’ expectations.

The recent movement in the stock suggests otherwise. Still, Buffett’s hefty purchases might indicate that the recent rise in Apple’s shares was caused not by the market’s optimism, but by Buffett’s. There were 19 trading days in the month of Jan. before Apple reported its earnings on the last day of the month. That works out to Berkshire buying an average of nearly 3.8 million shares a day. During that period, just over 27 million shares of Apple’s stock traded per day, meaning Buffett accounted for 14% of daily purchases on average.

That may not be enough to fully explain Apple’s recent stock market rise—particularly given the fact that its shares have jumped another $15, to $137, since Buffett stopped buying.

But add to that the purchases of the loyal investors who saw Buffett’s Apple purchases last year and followed him in the investment as well, and there is a case to be made that a good portion of the optimism around Apple these days could just be because of Oracle of Omaha’s eye.