BlackRock’s managing director Andrew Ang is urging investors to be cautious in how they return to the long-underperforming value factor, according to a recent article in Institutional Investor.

Although several big-name factor investors argue it’s time for investors to buy inexpensive value stocks—including AQR’s Cliff Asness and Research Affiliates founder Rob Arnott—Ang warns to exercise caution, suggesting that some might be tempted to “buy into the value factor simply because it appears inexpensive,” the article reports.

In a recent interview, Ang said, “Human behavior may cause us to foolishly get too excited about this. We all want to believe it’s time for value again, but our model says to be more cautious—we have increased our weight to value, but we don’t want to be massively overweight. BlackRock is trying to protect against human behavior that’s causing some of the premium in the first place.”

Still, Ang contends that investors shouldn’t give up on value, arguing “There is a lot of style drift among value managers and they haven’t all experienced the same gains.” While Ang sees risk in being short or not holding any value in a portfolio, he adds, “but let’s be precise about how we tilt back into the factor.”