Petaluma networking technology supplier Cyan warned investors Monday that revenues fell unexpectedly in the fourth quarter, the result of a sharp decline in orders from its largest customer.

The company now projects fourth-quarter revenues in the range of $20 million to $21 million, below the company's previous guidance of $30 million to $33 million. It will release year-end results next month.

Cyan stock dropped more than 22 percent following the disclosure, to $4 a share in after-hours trading. Before the announcement, Cyan shares had closed at $5.17 Monday on the New York Stock Exchange.

The company's largest customer, which was not identified, spent only $2 million with Cyan in the fourth quarter, down from $19 million in the third quarter. CEO Mark Floyd warned that revenue from the customer will continue to fluctuate from quarter to quarter.

"As we previously noted, our business in the near term is substantially dependent on this customer while we ramp revenue from new accounts and expand our customer base," Floyd said in a statement.

Excluding that customer, Cyan expects to increase its annual revenues by 32 to 34 percent, Floyd said.