Shares of Apple cratered nearly 8 percent in extended trading Wednesday — knocking some $50 billion off the market cap after the company took the unusual step of cutting its revenue guidance.

In a letter to investors, Cook said that Apple expects to report $84 billion in revenue during its next earnings report — it previously forecasted $91 billion.

Cook placed the blame on “both macroeconomic and Apple-specific factors,” and said that the iPhone maker failed to “foresee the magnitude of the economic deceleration” in emerging markets. Cook said that “over 100 percent” of Apple’s worldwide revenue decline “occurred in Greater China across iPhone, Mac and iPad.” He also cited the reduced prices for battery replacements causing customers to prolong the life of their older phones as a cause for the decline.

Read more at NY POST.