Facebook is planning to move its WhatsApp messaging service from IBM’s cloud to its own data centers, according to a report this week by CNBC.

WhatsApp, with its 1.2 billion uses, was at one time one of IBM’s top five cloud customers in terms of revenue, spending $2 million a month with IBM. It is no longer in the top five, according to CNBC sources.

The move is not necessarily surprising; when Facebook acquired WhatsApp in 2014, it was already in the process of migrating Instagram from AWS to its own data centers, according to the report. IBM told CNBC that it is “completely natural for Facebook to seek synergies” across its business.

In an off-the-record case study, IBM said that WhatsApp runs across more than 700 servers split between data centers in San Jose, California, and Washington, D.C., CNBC reports.

With around two times the number of users as Dropbox, it seems that WhatsApp’s cloud bill could have been hefty. Facebook also has realized a lot of efficiencies within its own infrastructure through custom designed servers, switches, power supplies and UPS units. [For more on Facebook data centers, check out the Data Center Knowledge Facebook Data Center FAQ]

Companies like Dropbox have been moving workloads from public cloud to on-premise infrastructure, citing cost savings, using the public cloud where it makes sense as part of a hybrid approach.

Last month, IBM Cloud signed a $700 million cloud partnership deal with Bombardier.