GHCi panics, though project builds just fine.

Summary

For the haskell-cpython project, attempting to launch GHCi causes a panic, although I can build the project without issue.

Steps to reproduce

1. Clone the GitHub repository above.
2. Move into the top level directory of the newly cloned repository.
3. Execute: stack setup.
4. Execute: stack build. (Note that it succeeds.)
5. Execute: stack ghci. (Observe the panic.)

Expected behavior

I expect it to cause a GHC panic.

I want it to launch a GHCi session w/ my packages imported and ready to go.

Environment

• GHC version used: 8.4.4 (Stack resolver LTS-12.18)

Optional:

• Operating System: MacOS X 10.14.5 (Mojave)
• System Architecture: MacBook Pro (<1yr. old; 32 GBytes RAM)