A new survey debunks rumors that women don’t stand up for themselves when it comes to pay. That said, there’s a caveat: Women haggle more than men when salaries specifically state they’re negotiable in help wanted ads.

When instructions aren’t as explicit and the pay is more ambiguous, the report revealed that men haggle more than women.

We heard about this in The Wall Street Journal @Work blog but the new report issued by the National Bureau of Economic Review reviewed 2,400 responses to help wanted ads for admin assistants in nine U.S. cities.

Some of the ads specifically pointed out that wages were negotiable whereas other ads were much more vague with salary and didn’t indicate the word “negotiable.”

Researchers concluded that women were nine percent more likely than men to negotiate when they had permission to do so. However, when salary requirement rules were more ambiguous, men were 29 percent more likely than women to haggle for a better package.

Researchers concluded that men prefer job environments where comp details are ambiguous and the same situation is a deterrent for women.