Roku (ROKU) - Get Report  shares fell sharply premarket Monday after the TV-streaming-hardware maker was downgraded to underweight from equal weight at Morgan Stanley. 

Analyst Benjamin Swinburne did raise his price target on the Los Gatos, Calif., company, to $110 a share from $100. 

"Roku continues to execute a sound strategy to capitalize on the shift to streaming," the analyst wrote. But he sees "risks to growth expectations not reflected in current valuation levels. Specifically, we think revenue and gross-profit growth slow meaningfully in '20, and the multiple compresses." 

Roku's platform sales multiple is about triple that of Netflix (NFLX) - Get Report  and nearly double that of high-growth software-as-a-service companies. 

"Roku shares are up over 400% year to date due to rising estimates and overall exuberance over all things streaming," Swinburne said in a note titled, "It's all priced in." 

"As a result, we see the risk/reward skewed to the downside. Roku's valuation levels have surged past digital media players and even past high-growth [software as a service] companies ... despite structurally lower gross margins." 

Roku's stock runup has some investors spooked as its earnings multiple gets stretched. Roku shares dipped in November, but the stock is up more than 10% over the past four weeks. 

Roku shares at last check were down 13.6% to $138.53.