When comparing smoker populations to the number of Obamacare enrollees who admit to smoking, it appears a significant amount of people are hiding the fact that they smoke from insurers.

Going by the number of Obamacare enrollees who pay a smoker surcharge, the average smoker population by state should be 8.3%. That number is inconsistent with CDC data, which says that the average smoker population by state is actually more than double that number at 19.4%. “Given how low these numbers are,” assistant health economics professor Cameron Kaplan told Kaiser Health News, “it’s hard to believe there is not some misrepresentation or lying going on.”

Smokers tend to have more expensive medical bills than non-smokers, considering all of the adverse effects smoking has on one’s health. So when they don’t pay their smoker surcharges, which are meant to offset those additional health costs, non-smokers end up paying more than they should.

Unfortunately, this problem isn’t a fixable one under the Affordable Care Act. Insurers have to rely on the honor system, and can’t legally check whether individuals are lying about their smoking habits. However, if they do somehow discover that an enrollee was lying, they can retroactively charge them.