diff --git a/dependent-sum.cabal b/dependent-sum.cabal
--- a/dependent-sum.cabal
+++ b/dependent-sum.cabal
@@ -1,5 +1,5 @@
 name:                   dependent-sum
-version:                0.2.0.2
+version:                0.2.1.0
 stability:              provisional
 
 cabal-version:          >= 1.6
diff --git a/src/Data/GADT/Compare.hs b/src/Data/GADT/Compare.hs
--- a/src/Data/GADT/Compare.hs
+++ b/src/Data/GADT/Compare.hs
@@ -4,6 +4,9 @@
 {-# OPTIONS_GHC -fno-warn-deprecated-flags #-}
 {-# LANGUAGE ImpredicativeTypes #-}
 {-# LANGUAGE CPP #-}
+#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 708
+{-# LANGUAGE PolyKinds #-}
+#endif
 #if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 702
 {-# LANGUAGE Safe #-}
 #endif