Shares of Dell and HP fell on Wednesday after the personal computer makers issued forecasts that cast doubt on a market recovery driven by artificial intelligence-enabled PCs.

Dell indicated the AI market was a “robust opportunity,” despite the company’s COO warning its AI business would “not be linear.”

Dell forecast fourth-quarter revenue below Wall Street expectations on Tuesday, weighed down by weaker demand for its traditional PCs and competition from rival server makers, sending its shares down more than 10% in extended trading.

While signs of a global PC market rebound began to materialise this year, shipments again dipped in the third quarter, according to IDC.