In a recent article for The Wall Street Journal, Burton Malkiel, author of the celebrated market tome A Random Walk Down Wall Street, wrote that “Investors have reason to worry.”

The chief investment officer of Wealthfront argues that all asset classes appear to be overpriced at the moment, and that an investor’s best defense in the effort to control risk should include both diversification and rebalancing.

“Broad diversification,” writes Malkiel, “is rightly known as ‘the only free lunch’ offered by financial markets.” He points out that, historically, investors have enjoyed smoother sailing, both on the gain and loss side of things, when their portfolios were diversified. Malkiel underscores the importance of international diversification, asserting that most investors suffer from a “home country” bias and that foreign stocks are more attractively valued than domestics.

On rebalancing, the author contends: “It’s a good idea to examine your portfolio periodically to ensure your asset allocation has not strayed far from your desired levels. He concludes by highlighting the importance of evaluating investment costs. “If you are paying an investment adviser 1% and your mutual funds have a 1% annual expense ratio, then fees will eat up a large part of that low-single-digit-return. The one thing I’m certain of is that minimizing costs is a winning strategy.”