diff --git a/Data/Proxy.hs b/Data/Proxy.hs
--- a/Data/Proxy.hs
+++ b/Data/Proxy.hs
@@ -1,4 +1,7 @@
-{-# LANGUAGE CPP, GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE CPP #-}
+#ifdef LANGUAGE_DeriveDataTypeable
+{-# LANGUAGE DeriveDataTypeable #-}
+#endif
 ----------------------------------------------------------------------------
 -- |
 -- Module     : Data.Proxy
@@ -7,7 +10,7 @@
 --
 -- Maintainer  : Edward Kmett <ekmett@gmail.com>
 -- Stability   : experimental
--- Portability : generalized newtype deriving
+-- Portability : portable
 --
 -------------------------------------------------------------------------------
 
@@ -38,7 +41,7 @@
 data Proxy p = Proxy deriving 
   ( Eq, Ord, Show, Read
 #ifdef LANGUAGE_DeriveDataTypeable
-  , Data,Typeable
+  , Data, Typeable
 #endif
   )
 
diff --git a/Data/Tagged.hs b/Data/Tagged.hs
--- a/Data/Tagged.hs
+++ b/Data/Tagged.hs
@@ -1,4 +1,7 @@
 {-# LANGUAGE CPP #-}
+#ifdef LANGUAGE_DeriveDataTypeable
+{-# LANGUAGE DeriveDataTypeable #-}
+#endif
 ----------------------------------------------------------------------------
 -- |
 -- Module     : Data.Tagged
@@ -7,7 +10,7 @@
 --
 -- Maintainer  : Edward Kmett <ekmett@gmail.com>
 -- Stability   : experimental
--- Portability : generalized newtype deriving
+-- Portability : portable
 --
 -------------------------------------------------------------------------------
 
@@ -30,6 +33,7 @@
 import Data.Data (Data,Typeable)
 #endif
 import Data.Ix (Ix(..))
+import Data.Monoid
 
 -- | A @'Tagged' s b@ value is a value @b@ with an attached phantom type @s@.
 -- This can be used in place of the more traditional but less safe idiom of
@@ -55,6 +59,10 @@
     readsPrec d = readParen (d > 10) $ \r ->
         [(Tagged a, t) | ("Tagged", s) <- lex r, (a, t) <- readsPrec 11 s]
 
+instance Monoid a => Monoid (Tagged s a) where
+    mempty = Tagged mempty
+    mappend (Tagged a) (Tagged b) = Tagged (mappend a b)
+
 instance Functor (Tagged s) where 
     fmap f (Tagged x) = Tagged (f x)
     {-# INLINE fmap #-}
@@ -97,7 +105,7 @@
     sequence (Tagged x) = liftM Tagged x
     {-# INLINE sequence #-}
 
-instance (Enum a) => Enum (Tagged s a) where
+instance Enum a => Enum (Tagged s a) where
     succ = fmap succ
     pred = fmap pred
     toEnum = Tagged . toEnum
@@ -108,7 +116,7 @@
     enumFromThenTo (Tagged x) (Tagged y) (Tagged z) =
         map Tagged (enumFromThenTo x y z)
 
-instance (Num a) => Num (Tagged s a) where
+instance Num a => Num (Tagged s a) where
     (+) = liftA2 (+)
     (-) = liftA2 (-)
     (*) = liftA2 (*)
@@ -117,10 +125,10 @@
     signum = fmap signum
     fromInteger = Tagged . fromInteger
 
-instance (Real a) => Real (Tagged s a) where
+instance Real a => Real (Tagged s a) where
     toRational (Tagged x) = toRational x
 
-instance (Integral a) => Integral (Tagged s a) where
+instance Integral a => Integral (Tagged s a) where
     quot = liftA2 quot
     rem = liftA2 rem
     div = liftA2 div
@@ -131,12 +139,12 @@
         (a, b) = divMod x y
     toInteger (Tagged x) = toInteger x
 
-instance (Fractional a) => Fractional (Tagged s a) where
+instance Fractional a => Fractional (Tagged s a) where
     (/) = liftA2 (/)
     recip = fmap recip
     fromRational = Tagged . fromRational
 
-instance (Floating a) => Floating (Tagged s a) where
+instance Floating a => Floating (Tagged s a) where
     pi = Tagged pi
     exp = fmap exp
     log = fmap log
@@ -156,7 +164,7 @@
     (**) = liftA2 (**)
     logBase = liftA2 (**)
 
-instance (RealFrac a) => RealFrac (Tagged s a) where
+instance RealFrac a => RealFrac (Tagged s a) where
     properFraction (Tagged x) = (a, Tagged b) where
         (a, b) = properFraction x
     truncate (Tagged x) = truncate x
@@ -164,7 +172,7 @@
     ceiling (Tagged x) = ceiling x
     floor (Tagged x) = floor x
 
-instance (RealFloat a) => RealFloat (Tagged s a) where
+instance RealFloat a => RealFloat (Tagged s a) where
     floatRadix (Tagged x) = floatRadix x
     floatDigits (Tagged x) = floatDigits x
     floatRange (Tagged x) = floatRange x
@@ -209,4 +217,3 @@
 untagSelf :: Tagged a a -> a
 untagSelf (Tagged x) = x
 {-# INLINE untagSelf #-}
-
diff --git a/tagged.cabal b/tagged.cabal
--- a/tagged.cabal
+++ b/tagged.cabal
@@ -1,27 +1,30 @@
 name:           tagged
-version:        0.4.1
+version:        0.4.2
 license:        BSD3
 license-file:   LICENSE
 author:         Edward A. Kmett
 maintainer:     Edward A. Kmett <ekmett@gmail.com>
 stability:      experimental
 category:       Data, Phantom Types
-synopsis:       Provides newtype wrappers for phantom types to avoid unsafely passing dummy arguments
+synopsis:       Haskell 98 phantom types to avoid unsafely passing dummy arguments
 homepage:       http://github.com/ekmett/tagged
 copyright:      2009-2011 Edward A. Kmett
-description:    Provides newtype wrappers for phantom types to avoid unsafely passing dummy arguments
+description:    Haskell 98 phantom types to avoid unsafely passing dummy arguments
 build-type:     Simple
-cabal-version:  >=1.6
+cabal-version:  >= 1.10
 
 source-repository head
   type: git
   location: git://github.com/ekmett/tagged.git
 
 library
+  default-language: Haskell98
+  other-extensions: CPP
   if !impl(hugs)
     cpp-options: -DLANGUAGE_DeriveDataTypeable
-    extensions: DeriveDataTypeable
-  build-depends: base >= 2 && < 5
+    other-extensions: DeriveDataTypeable
+  build-depends:
+    base >= 2 && < 5
   exposed-modules:
     Data.Tagged
     Data.Proxy