GHC rejects typeclass with associated type

In GHC 7.8.4, the following code is legal:

{-# LANGUAGE TypeFamilies, FlexibleContexts #-}
    
class FiniteGrid g where
  type Size s
  size :: g -> Size g
  maxPossibleDistance :: g -> Int

But with GHC 7.10.1, it no longer compiles. The error message is:

The associated type ‘Size’
mentions none of the type or kind variables of the class ‘FiniteGrid g’
In the class declaration for ‘FiniteGrid’

I didn't see any mention of this in the migration guide, but perhaps there's another pragma I need to enable. I thought this might be related to #10020 (closed), but that bug is apparently fixed in GHC 7.10.1.

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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