Apple lost $6 billion in sales during the tech giant’s fourth fiscal quarter as it was besieged by supply chain problems that missed Wall Street forecasts, and Apple CEO Tim Cook said the impact will be even worse in the current Christmas quarter.

Cook said Thursday that the quarter ended September 25 had “larger than expected supply constraints” worsened by pandemic-related production disruptions in Southeast Asia. Cook also noted that while Apple had seen “significant improvement” at its Southeast Asian plants by the end of October, the chip shortage remained unresolved and is now affecting “most of our products.”

Apple is forecasting growth of 7.4% expansion to $119.7 billion for its December quarter.

Shares of the technology giant, which have risen 15% this year, fell 3.4% in extended trading on Thursday, a drop that could make Microsoft Corp the world’s most valuable company after a run on Microsoft shares and ride the surge in its cloud computing business.

Apple fell short of expectations in two key areas.

Apple said fourth-quarter iPhone sales were $38.9 billion, below its original forecast of $41.5 billion.

Apple’s accessories sector, which includes fast-growing categories such as the AirPods wireless headphones, was $500 million below analyst forecasts of $9.3 billion, according to Refinitiv data.