1 files changed, 4 insertions, 1 deletions
diff --git a/libraries/base/GHC/IOArray.hs b/libraries/base/GHC/IOArray.hs
index ff9e545817..33b1804dbb 100644
--- a/libraries/base/GHC/IOArray.hs
+++ b/libraries/base/GHC/IOArray.hs
@@ -1,5 +1,5 @@
 {-# LANGUAGE Unsafe #-}
-{-# LANGUAGE NoImplicitPrelude, AutoDeriveTypeable #-}
+{-# LANGUAGE NoImplicitPrelude, AutoDeriveTypeable, RoleAnnotations #-}
 {-# OPTIONS_GHC -funbox-strict-fields #-}
 {-# OPTIONS_HADDOCK hide #-}
 
@@ -41,6 +41,9 @@ import Data.Typeable.Internal
 
 newtype IOArray i e = IOArray (STArray RealWorld i e) deriving( Typeable )
 
+-- index type should have a nominal role due to Ix class. See also #9220.
+type role IOArray nominal representational
+
 -- explicit instance because Haddock can't figure out a derived one
 instance Eq (IOArray i e) where
   IOArray x == IOArray y = x == y