Shares of Fitbit plunged in trading Thursday, after the wearable tech company shocked investors with a disappointing forecast for the holiday quarter.

Fitbit’s fit stock fell an unprecedented 30% after its third quarter earnings report Wednesday. Although the company’s third quarter earnings were in-line with analyst estimates, Fitbit said it expected sales to grow just 2-5% compared to the same period last year. The forecast was a considerable downgrade to what Fitbit had managed to show investors in 2015—a 92% increase in sales.

The news also brought down GoPro’s gpro stock 6% in trading Thursday. Shares of GoPro and Fitbit have a correlation coefficient of 0.89 out of 1, according to FactSet.

GoPro is expected to report its fourth-straight quarter of sales declines after the market closes Thursday. The action camera company has struggled to reach a larger consumer base, and has recently tried tapping into the drone market.

 

Wall Street expects GoPro to deliver $313.3 million in sales, down 21% from last year, and a loss of $0.36 per share, down from a profit of $0.25 per share last year.

Analysts are keeping a close eye on the critical holiday shopping season, when sales of GoPro’s new camera, the Hero5, and drone, Karma, will show up in earnings.

Shares of GoPro have fallen 66% since its IPO in 2014.