DeriveAnyClass + deriving Bifunctor causes GHC panic

Attempting the derive Bifunctor with DeriveAnyClass caused this message from GHC:

$ ghc Foo.hs
[1 of 1] Compiling Foo              ( Foo.hs, Foo.o )
Var/Type length mismatch:
  [a_an7, b_an8]
  []
Var/Type length mismatch:
  [a_an7, b_an8]
  []
Var/Type length mismatch:
  [a_an7, b_an8]
  []

Foo.hs:8:13:ghc: panic! (the 'impossible' happened)
  (GHC version 7.10.2 for x86_64-apple-darwin):
	tcTyVarDetails a_an7

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

The code:

{-# LANGUAGE DeriveAnyClass #-}

module Foo where

import Data.Bifunctor

data Blah a b = A a | B b
  deriving (Bifunctor)

Trac metadata

Trac field	Value
Version	7.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	MacOS X
Architecture