One of the big advantages of Google Fi is its flexibility. You just pay for the data you use at a rate of $10 a gig, up to a recently-set maximum of $80 a month. But, according to a lawsuit filed earlier this week, Google may have charged at least one Project Fi subscriber for data that was used while the customer was on a Wi-Fi connection. 

The Register was the first to report on the news yesterday, and it’s a bit disconcerting. It’s possible to see how this type of billing mistake might happen, though, based on how Google tracks data usage. It could be since Fi is an MVNO (a mobile virtual network operator that leases other networks for service), but apparently, Project Fi keeps track of data used on the device itself, rather than at the network level.

Even though Google explicitly states customers “are not charged for the data [they] use when connected to open or home Wi-Fi,” at least one subscriber named in the suit claims to have been billed to the tune of $200 in overages for data not served by Fi. The complaint also cites other public accounts of similar problems posted to venues such as Reddit.

While there doesn’t seem to be any evidence just yet that the alleged problem is affecting a large number of subscribers, the suit does claim that the issue is widespread and that at some level Google acknowledged that the billing errors were a known issue. To that end, it might be a good idea to keep an eye on your billed data if you’re a Project Fi subscriber.