On the surface, it’s always looked like Apple and Google are mortal enemies. Android vs iOS, Siri vs Assistant, mythical AR glasses vs Google Glass — there’s a lot of competition going on there.

But deeper down, both tech companies are partners as well as rivals. Google pays Apple $3 billion a year to remain the default search option on iOS, and according to a file on Apple’s website, some of that money goes back the other way to pay for iCloud storage on Google’s public cloud.

According to CNBC, changes were made to the iOS Security Guide last month, a white paper that Apple maintains to provide information on its security policies. A section on data storage removed any references to Microsoft’s Azure platform, and instead replaced them with references to the Google Cloud Platform. That indirectly confirms reporting from 2016 that suggested iCloud data was stored on Google’s cloud.

There’s no indication of whether Apple is simply using Google’s cloud for cheap and efficient storage of photos and backups, or whether Google’s more advanced cloud features are coming into play.

Google’s Cloud Platform has become an increasingly significant part of the company’s revenue in recent years. Despite a slow start compared to Amazon Web Services and Microsoft Azure, Google’s corporate-level cloud platform brought in nearly $4 billion in revenue last year. Customers for the cloud platform include Spotify, PayPal, and Snap.