diff --git a/src/Data/Validity.hs b/src/Data/Validity.hs
--- a/src/Data/Validity.hs
+++ b/src/Data/Validity.hs
@@ -64,14 +64,18 @@
     , Monoid(..)
     ) where
 
-import Debug.Trace
 
 import Data.Either (isRight)
 import Data.Fixed (Fixed(MkFixed), HasResolution)
 import Data.List (intercalate)
+#if MIN_VERSION_base(4,9,0)
 import Data.List.NonEmpty (NonEmpty((:|)))
+#endif
 import Data.Maybe (Maybe, fromMaybe)
+#if MIN_VERSION_base(4,8,0)
+#else
 import Data.Monoid
+#endif
 import Data.Word (Word, Word16, Word32, Word64, Word8)
 import GHC.Generics
 #if MIN_VERSION_base(4,8,0)
@@ -186,7 +190,7 @@
 
 instance Validity ValidationChain
 
-data Validation = Validation
+newtype Validation = Validation
     { unValidation :: [ValidationChain]
     } deriving (Show, Eq, Generic)
 
@@ -372,9 +376,13 @@
         map
             (\(ix, e) ->
                  e <?!>
-                 (unwords ["The element at index", show ix, "in the list"])) .
+                 unwords
+                 [ "The element at index"
+                 , show (ix :: Integer)
+                 , "in the list"]) .
         zip [0 ..]
 
+#if MIN_VERSION_base(4,9,0)
 -- | A nonempty list is valid if all the elements are valid.
 --
 -- See the instance for 'Validity [a]' for more information.
@@ -385,6 +393,7 @@
             [ e <?!> "The first element of the nonempty list"
             , es <?!> "The rest of the elements of the nonempty list"
             ]
+#endif
 
 -- | A Maybe thing is valid if the thing inside is valid or it's nothing
 -- It makes sense to assume that 'Nothing' is valid.
@@ -585,7 +594,7 @@
 prettyValidation :: Validity a => a -> Either String a
 prettyValidation a =
     case checkValidity a of
-        Right a -> Right a
+        Right a_ -> Right a_
         Left errs -> Left $ intercalate "\n" $ map (errCascade . toStrings) errs
   where
     toStrings (Violated s) = ["Violated: " ++ s]
diff --git a/validity.cabal b/validity.cabal
--- a/validity.cabal
+++ b/validity.cabal
@@ -1,5 +1,5 @@
 name: validity
-version: 0.4.0.1
+version: 0.4.0.2
 cabal-version: >=1.10
 build-type: Simple
 license: MIT