Costco (COST) - Get Report  was falling after shares of the warehouse retailer were downgraded by analysts at Oppenheimer who are worried about valuation following the stock's nearly 50% year-to-date increase. 

Oppenheimer downgraded the stock to perform from outperform, leading to a 0.73% decline in trading Wednesday to $294.83. Despite the downgrade, Oppenheimer raised Costco's price target to $300 from $295. 

The price target represents very little upside from the stock's previous closing price of $297. 

"As we look forward, we now see less upside for shares driven by the now even more premium valuation, potentially aggressive Street forecasts, and difficult compares especially in Q2," Oppenheimer analyst Rupesh Parikh said. 

The company's price to future earnings ratio sits at 34.5 times, which is "well above prior peaks on both metrics," according to Parikh. 

Oppenheimer has full year 2020 and 2021 earnings estimates of $8.40 and $8.95 a share, below consensus estimates of $8.55 and $9.21 per share, respectively.