Apple's (AAPL) - Get Reportbig drop on Thursday following its surprise revenue warning has been costly for the Oracle of Omaha. 

Berkshire Hathaway's (BRK.B) - Get Report roughly 5.3% stake in the tech giant declined by about $4 billion on Thursday morning, based on Berkshire's reported holdings as of Sept. 30. Berkshire owns about 252 million shares of Apple, which was worth about $39.8 billion prior to Apple's revenue warning on late Wednesday afternoon. On Thursday, following Apple's 10% decline, those shares were worth $35.8 billion, however.  

Shares of Berkshire were down 5.4% to $191.90 on Thursday.   

Buffett, who famously avoided investing in tech stocks for decades, first began amassing a position in Apple in mid-2016 and has been steadily adding to it since then.

The other current top holders of Apple's stock are all mutual funds. Vanguard is the largest owner of Apple stock, with 332 million shares as of Sept. 30, followed by Berkshire, BlackRock with 199.6 million shares, State Street with 192.5 million shares and Fidelity with 103.4 million shares.

Jim Cramer's Action Alerts Plus team, which owns Apple in its portfolio, notes that "our initial reaction is that longer term, despite the cut, we still believe that Apple is doing the right thing regarding its efforts to switch the narrative from one based on hardware sales to one based primarily on recurring Services revenues." (To read Jim and his Action Alerts PLUS team's full note on Apple's announcement, click here).