SAN FRANCISCO (AP) — Apple warns that disappointing iPhone sales will cause a significant drop in its revenue over the crucial holiday season compared to earlier projections.

CEO Tim Cook made the announcement after the market closed Wednesday. It embodies some of the worst fears of investors, who have been dumping Apple shares amid signs that the latest iPhone models weren’t living up to expectations.

Cook cited China as Apple’s biggest weak spot, but also said that consumers weren’t upgrading to the latest iPhones models as eagerly as anticipated.

As a result, Apple now expects revenue of $84 billion for the fiscal quarter running from October through December. Management had previously predicted revenue ranging from $89 billion to $93 billion.