Major market indexes may be reaching record highs, but many investors aren’t feeling optimistic right now.

The CNN Fear & Greed Index, which measures investor sentiment over time, has been steadily dropping over the last month. On May 1, the index peaked at 71 — firmly in the “greed” category. By mid-May, it had dropped to 63. As of this writing, it sits at 55. While that’s still in the “neutral” category for now, it’s inching its way closer to the “fear” side of the spectrum.

To be clear, this doesn’t mean that a recession is around the corner. But if you’re feeling nervous about investing right now, you’re not alone. Here’s Warren Buffett’s best advice for situations like these.

One of Warren Buffett’s most timeless pieces of investing advice is to “be greedy when others are fearful.” In other words, when other investors may be tempted to get out of the market, that’s the best opportunity to dig in and invest more.

He offered this advice in a 2008 opinion piece for The New York Times, when investor sentiment was at rock bottom amid the Great Recession.

“[F]ear is now widespread, gripping even seasoned investors,” he noted. “But fears regarding the long-term prosperity of the nation’s many sound companies make no sense. These businesses will indeed suffer earnings hiccups, as they always have. But most major companies will be setting new profit records five, 10, and 20 years from now.”

Buffett’s prediction came true, and the S&P 500 (^GSPC 2.64%) has soared by over 1,000% since that article was published in October 2008. Those who followed Buffett’s advice and continued investing — even when the market was in a free fall — would have earned lucrative long-term returns.

^SPX data by YCharts

While nobody can say exactly when the next downturn will begin, the market will eventually face a pullback. And when it does, that will be a fantastic opportunity to “be greedy” and load up on high-quality stocks at steep discounts.

And if stocks continue to thrive for several more months or even years, continuing to invest now will set you up to take advantage of those gains.

If history shows us anything, it’s that consistent investing — no matter what the market’s doing in the short term — is the most effective way to capitalize on its long-term growth potential. By building a healthy portfolio full of robust stocks, you’ll be well-positioned to weather any potential volatility and generate long-term wealth.