If history is any guide, says MarketWatch’s Mark Hulbert, stocks are likely to struggle in September but then rebound and end the year above where they were on Labor Day.

“Since 1896, when the Dow Jones Industrial Average was created, there has been a markedly better chance of the market rising over the last four months of the year whenever stocks were ahead for the year-to-date period through Labor Day,” Hulbert writes. In years when the Dow has been in positive year-to-date territory on Labor Day, it has gained ground from Labor Day through the end of the year 70% of the time Hulbert says; the average return in those years was 3.7% from Labor Day through year-end. In years when the index has been in the red year-to-date on Labor Day, it has climbed higher just 51% of the time; the average return in those years was -2.1% from Labor Day through year-end.

Hulbert says those numbers are statistically significant. But he also says that, historically, even when stocks have been in positive territory on Labor Day, they’ve still tended to lose ground in September. That, combined with what he says is too much bullishness in the market, lead Hulbert to hypothesize that the market will endure some weakness in September, but then more than make up for it with gains later in the year.