diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,7 @@
+4.0.2
+-----
+* Made := kind polymorphic.
+
 4.0.1
 -----
 * Provided an explicit nominal `RoleAnnotation`.
diff --git a/eq.cabal b/eq.cabal
--- a/eq.cabal
+++ b/eq.cabal
@@ -1,6 +1,6 @@
 name:          eq
 category:      Type System
-version:       4.0.1
+version:       4.0.2
 license:       BSD3
 cabal-version: >= 1.6
 license-file:  LICENSE
diff --git a/src/Data/Eq/Type.hs b/src/Data/Eq/Type.hs
--- a/src/Data/Eq/Type.hs
+++ b/src/Data/Eq/Type.hs
@@ -2,6 +2,9 @@
 #if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 702
 {-# LANGUAGE Trustworthy #-}
 #endif
+#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 706
+{-# LANGUAGE PolyKinds #-}
+#endif
 #if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 707
 {-# LANGUAGE RoleAnnotations #-}
 #endif