diff --git a/src/Data/AdditiveGroup.hs b/src/Data/AdditiveGroup.hs
--- a/src/Data/AdditiveGroup.hs
+++ b/src/Data/AdditiveGroup.hs
@@ -13,10 +13,11 @@
 
 module Data.AdditiveGroup
   ( 
-    AdditiveGroup(..), (^-^), sumV
+    AdditiveGroup(..), (^-^), sumV, Sum
   ) where
 
 import Control.Applicative
+import Data.Monoid (Monoid(..))
 import Data.Complex hiding (magnitude)
 
 import Data.MemoTrie
@@ -40,6 +41,7 @@
 sumV :: AdditiveGroup v => [v] -> v
 sumV = foldr (^+^) zeroV
 
+
 instance AdditiveGroup () where
   zeroV     = ()
   () ^+^ () = ()
@@ -87,3 +89,21 @@
   zeroV   = pure   zeroV
   (^+^)   = liftA2 (^+^)
   negateV = fmap   negateV
+
+
+-- | Monoid under group addition.  Alternative to the @Sum@ in
+-- "Data.Monoid", which uses 'Num' instead of 'AdditiveGroup'.
+newtype Sum a = Sum a
+  deriving (Eq, Ord, Read, Show, Bounded)
+
+instance Functor Sum where
+  fmap f (Sum a) = Sum (f a)
+
+instance Applicative Sum where
+  pure a = Sum a
+  Sum f <*> Sum x = Sum (f x)
+
+instance AdditiveGroup a => Monoid (Sum a) where
+  mempty  = Sum zeroV
+  mappend = liftA2 (^+^)
+
diff --git a/vector-space.cabal b/vector-space.cabal
--- a/vector-space.cabal
+++ b/vector-space.cabal
@@ -1,5 +1,5 @@
 Name:                vector-space
-Version:             0.5
+Version:             0.5.1
 Cabal-Version:       >= 1.2
 Synopsis:            Vector & affine spaces, linear maps, and derivatives (requires ghc 6.9)
 Category:            math
@@ -14,9 +14,6 @@
   and requires ghc version at least 6.9.
   .
   Project wiki page: <http://haskell.org/haskellwiki/vector-space>
-  .
-  The module documentation pages have links to colorized source code and
-  to wiki pages where you can read and contribute user comments.  Enjoy!
   .
   &#169; 2008 by Conal Elliott; BSD3 license.
 Author:              Conal Elliott