Goldman Sachs analyst Toshiya Hari issued a rare “sell” recommendation to AMD investors, predicting that the stock could fall more than 20% to $11 a share. The report prompted plenty of immediate selling. Shares of AMD, which risen more than fivefold over the past year, were down 8% to $12.98 in midday trading on Thursday.

Investors had regained tremendous confidence in AMD and CEO Lisa Su over the past year as the company rolled out new products, increased its video game console revenue, and struck a deal to license some technology for server chips to a Chinese manufacturer. AMD hasn’t yet regained much market share from Intel in PC central processing units (CPUs) or Nvidia in graphics processing units (GPUs). But anticipation is building that AMD’s new Ryzen and Vega chip lines will make significant in roads in both areas.

Goldman analyst Hari warned, however, that the stock had risen too far too fast and AMD would not be able to meet expectations.

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“For the stock to continue to outperform, AMD needs to hit a number of lofty competitive and financial targets (i.e. regain high end CPU and GPU share and expand gross margins from 31.3% in CY16 to 36-40%),” Hari wrote. “Simply put, the bar is very high and we recommend investors sell the stock.”

One of the biggest challenges is that AMD (AMD) is seeking to win customers by pricing its chips far below the amounts charged by Intel (INTC) and Nvidia. The first Ryzen chips for desktop computers matched the performance of some high-end Intel chips at half the price, AMD said in February.

But Intel has already reduced its prices somewhat and had plenty of room to go lower, as will Nvidia (NVDA) with AMD’s Vega GPUs, Hari said.

“While we expect Intel and Nvidia to remain disciplined on pricing, if necessary, both companies have the capacity to compete on price given significantly higher gross margins,” Hari wrote.