cabal.exe: --enable-tests was specified, but tests can't be enabled in a remote package

The AppVeyor build currently fails with this message:

Building Haskell library
Downloading the latest package list from hackage.haskell.org
cabal.exe: --enable-tests was specified, but tests can't be enabled in a remote package

C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V140\Microsoft.CppCommon.targets(171,5): error MSB6006: "cmd.exe" exited with code 1.
[C:\projects\build\MSVC2015\x86\lib\hs\haskell_library.vcxproj]

I found this, but I am unsure what to do with that knowledge:
https://github.com/haskell/cabal/issues/5650

If any Haskellian likes to help out, please do.