The investment firm of the world’s most famous investor, Warren Buffett, has increased his stake in Apple even as other big investment funds have dumped the stock.

Buffett’s Berkshire Hathaway increased its stake in the iPhone maker from 9.8m shares to just over 15.3m shares in the second quarter of the year, according to a securities filing.

This represents an increase of 55 percent in his stake, which is now valued at around $1.675 billion.

Buffett disclosed in a regulatory filing in May that Berkshire Hathaway had acquired the original stake.

One of the most successful investors in history, Warren Buffett is sometimes known as the ‘Sage’ or ‘Oracle’ of Omaha.

This comes at a time when concerns about slow growth at the iPhone manufacturer have driven away other investors, including Greenlight Asset Management, which cut its Apple stake by 16 percent from the end of the first quarter to 6.855 million shares according to whalewisdom.com.

The hedge fund of George Soros, another well-known investor, also cut its stake in Apple. Carl Icahn revealed in April 2016 that he had sold off his entire stake in Apple.

Apple’s stock has risen 2 percent since the beginning of the year.

However, it has also reported declining revenues. In Q2, Apple reported a 13 percent decline in its revenue, its first fall in revenue since 2003. In its Q3 results, Apple saw sales of its iPhone fall for a second consecutive quarter. The company sold 40.4 million iPhones in Q3, down 15 percent from a year ago.

Like other vendors, Apple is having to navigate a wider slowdown in the smartphone market, which is approaching saturation point. In April, Strategy Analytics research found that global smartphone shipments fell 3 percent annually to reach 335 million units in Q1 2016, the first ever shrinking of the global smartphone market in history.