qtjsondb build error: Module jsondbpartition has no public API

I'm getting this:

error: Module jsondbpartition has no public API

when building qtjsondb, which is part of the default configuration in qt5.git/dev.

Here's a thread showing a couple of other people with the same problem:

http://www.qtcentre.org/threads/56170-Module-has-no-public-API

One of them suggests removing CONFIG += internal_module from src/partition/partition.pro, which fixed the problem for me.