Investment newsletter guru Dan Sullivan has changed his call on stocks from sell to buy.

Sullivan made the move on Monday night, Mark Hulbert wrote on Marketwatch. That decision has worked out so far, with the Standard & Poor’s 500 Index rising 0.36 percent Tuesday.

Sullivan, editor of The Chartist, is starting to resemble a yo-yo. Two weeks ago, he issued a sell signal. That call didn’t work out too well, as the S&P 500 has gained 8 percent since then.

But The Chartist has one of the best long-term stock market timing records of any investment newsletter tracked by the Hulbert Financial Digest.

At the moment, “it's impossible to know whether throwing in the towel on an unprofitable trade represents an admirable flexibility in the face of new information, or a foolish lack of discipline,” Hulbert points out.

“Sullivan's long-term record suggests, at a minimum, that we give him the benefit of the doubt.

“At least we now know that Sullivan is not suffering from the investment paralysis that Jeremy Grantham, the highly regarded chief investment strategist at GMO, warned investors about earlier this year,” Hulbert writes.

Sullivan isn’t the only trying on the bear suit these days.

David Hefty, principal of Cornerstone Wealth Management, tells CNBC that stocks’ recent gains represent merely a relief rally in a bear market that will last 10 to 15 years.