diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,7 @@
+0.3.1
+-----
+* Explicit nominal role annotation
+
 0.3.0.1
 -------
 * Nicer formatting of the haddocks
diff --git a/heaps.cabal b/heaps.cabal
--- a/heaps.cabal
+++ b/heaps.cabal
@@ -1,5 +1,5 @@
 name:           heaps
-version:        0.3.0.1
+version:        0.3.1
 license:        BSD3
 license-file:   LICENSE
 author:         Edward A. Kmett
diff --git a/src/Data/Heap.hs b/src/Data/Heap.hs
--- a/src/Data/Heap.hs
+++ b/src/Data/Heap.hs
@@ -1,4 +1,8 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE DeriveDataTypeable #-}
+#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 707
+{-# LANGUAGE RoleAnnotations #-}
+#endif
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.Heap
@@ -102,7 +106,11 @@
 data Heap a
   = Empty
   | Heap {-# UNPACK #-} !Int (a -> a -> Bool) {-# UNPACK #-} !(Tree a)
-  deriving (Typeable)
+  deriving Typeable
+
+#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 707
+type role Heap nominal
+#endif
 
 instance Show a => Show (Heap a) where
   showsPrec _ Empty = showString "fromList []"