Weird error while pushing / building on Heroku

[saurabhnanda]

Here's what I'm trying to deploy to Heroku - https://github.com/saurabhnanda/haskell-heroku

After limgmp is successfully compiled, the deployment fails with the following error message:

remote: -----> Downloading stack
remote: -----> Installing stack
remote: -----> Installing stack-run
remote: -----> Setting up stack
remote:        Downloading lts-12.1 build plan ...
remote:        Downloaded lts-12.1 build plan.
remote:        AesonException "Invalid flag name: \"bytestring--lt-0_10_4\""
remote:  !     Push rejected, failed to compile Stack app.
remote: 
remote:  !     Push failed