diff --git a/Text/IDNA.hs b/Text/IDNA.hs
--- a/Text/IDNA.hs
+++ b/Text/IDNA.hs
@@ -80,10 +80,5 @@
 mergeEither (Left x) = x
 mergeEither (Right y) = y
 
-instance Monad (Either a) where
-	return = Right
-	Left x >>= _ = Left x
-	Right y >>= f = f y
-
 tests :: [Text]
 tests = ["Bücher","tūdaliņ"]
diff --git a/idna.cabal b/idna.cabal
--- a/idna.cabal
+++ b/idna.cabal
@@ -1,5 +1,5 @@
 Name: idna
-Version: 0.1.1
+Version: 0.1.2
 Description: Implements IDNA -- Internationalized Domain Names in Applications (RFC 3490).
 Synopsis: Implements IDNA (RFC 3490).
 License: BSD3
@@ -11,6 +11,6 @@
 Category: Data, Text, RFC
 
 Library
- Build-Depends: base, encoding>=0.5.1, stringprep>=0.1.2, text>=0.1
+ Build-Depends: base >= 4.3 && < 5, encoding>=0.5.1, stringprep>=0.1.2, text>=0.1
  Exposed-modules: Text.IDNA
  ghc-options: -O2 -Wall