Tellabs (NASDAQ:TLAB) disclosed on Tuesday weaker-than-expected fourth-quarter results and a bleak outlook for the current quarter, sparking a 20% plunge in the network equipment maker’s stock price.

The Naperville, Ill.-based company said it lost $11 million, or 3 cents a share, last quarter, compared with a profit of $62 million, or 16 cents a share, a year earlier. Excluding one-time items, it earned 2 cents a share, widely trailing the Street’s view of 8 cents a share.

Sales rose 5.4% to $410.5 million, compared with consensus calls for $418.4 million.

Tellabs warned it expects first-quarter non-GAAP gross margins of 40%, plus or minus 2 points, on sales of $315 million to $335 million. Wall Street analysts had been forecasting much higher first-quarter sales of $402.7 million.

Shareholders punished Tellabs for the weaker-than-expected results and gloomy forecast, sending the company’s stock down 20.03% to $5.63 ahead of the opening bell.

“Tellabs’ fourth quarter brought revenue growth but a setback in profitability,” CEO Rob Pullen said in a statement. “Looking ahead, customers continue to validate Tellabs’ focus on the smart mobile Internet, and we remain focused on investing our way forward to pursue this growth opportunity.”