diff --git a/extensible-effects.cabal b/extensible-effects.cabal
--- a/extensible-effects.cabal
+++ b/extensible-effects.cabal
@@ -6,7 +6,7 @@
 -- PVP summary:      +-+------- breaking API changes
 --                   | | +----- non-breaking API additions
 --                   | | | +--- code changes with no API change
-version:             1.11.0.3
+version:             1.11.0.4
 
 -- A short (one-line) description of the package.
 synopsis:            An Alternative to Monad Transformers
@@ -43,7 +43,7 @@
 
 category:            Control, Effect
 
-tested-with:         GHC==7.10.3, GHC==7.10.1, GHC==7.8.4, GHC==7.6.3
+tested-with:         GHC==8.0.1, GHC==7.10.3, GHC==7.10.1, GHC==7.8.4, GHC==7.6.3
 
 build-type:          Simple
 
diff --git a/src/Data/OpenUnion.hs b/src/Data/OpenUnion.hs
--- a/src/Data/OpenUnion.hs
+++ b/src/Data/OpenUnion.hs
@@ -11,6 +11,10 @@
 {-# LANGUAGE FunctionalDependencies, UndecidableInstances #-}
 {-# LANGUAGE FlexibleContexts #-}
 
+#if __GLASGOW_HASKELL__ >= 800
+{-# LANGUAGE UndecidableSuperClasses #-}
+#endif
+
 #if __GLASGOW_HASKELL__ >= 708
 #define Typeable1 Typeable
 #endif
diff --git a/src/Data/OpenUnion/Internal/Base.hs b/src/Data/OpenUnion/Internal/Base.hs
--- a/src/Data/OpenUnion/Internal/Base.hs
+++ b/src/Data/OpenUnion/Internal/Base.hs
@@ -10,6 +10,10 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE Trustworthy #-} -- GHC.Exts.Constraint makes module not 'Safe'
 
+#if __GLASGOW_HASKELL__ >= 800
+{-# LANGUAGE UndecidableSuperClasses #-}
+#endif
+
 #if __GLASGOW_HASKELL__ >= 708
 #define Typeable1 Typeable
 #endif
diff --git a/src/Data/OpenUnion/Internal/OpenUnion2.hs b/src/Data/OpenUnion/Internal/OpenUnion2.hs
--- a/src/Data/OpenUnion/Internal/OpenUnion2.hs
+++ b/src/Data/OpenUnion/Internal/OpenUnion2.hs
@@ -11,6 +11,12 @@
 -- Only for MemberU below, when emulating Monad Transformers
 {-# LANGUAGE FunctionalDependencies, UndecidableInstances #-}
 
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__ >= 800
+{-# LANGUAGE UndecidableSuperClasses #-}
+#endif
+
+
 -- | Original work at <http://okmij.org/ftp/Haskell/extensible/OpenUnion2.hs>.
 -- Open unions (type-indexed co-products) for extensible effects.
 -- This implementation relies on _closed_ type families added to GHC 7.8. It has