compiler crash building hashed-storage 0.5.3

ghc: panic! (the 'impossible' happened)
  (GHC version 7.0.0.20100924 for x86_64-unknown-linux):
        Expected one of wanted constraints (BUG)

This happens with cabal install hashed-storage-0.5.3, but that's a bit of a pain to reproduce as it depends on dataenc which needs a dependency bump. I cut it down to the attached file which just depends on mtl.

Trac metadata

Trac field	Value
Version	6.13
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	ganesh
Operating system
Architecture