The federal website central to Obamacare has been operating with a calculating error that could have negatively affected enrollment numbers, and no one seemed to know about it for nearly six months.

The Philadelphia Inquirer reports that HealthCare.Gov has a little-known glitch in its subsidy calculator that, though quite small, may be notifying people who are eligible for financial assistance that they do not qualify for a subsidy. The site’s calculator is an unofficial estimate that consumers can use to see how much financial assistance they qualify for before beginning the application process.

So, the glitch isn’t causing people to receive inaccurate subsidies, it’s just providing them with inaccurate information before they make the decision to move forward in the application process.