diff --git a/Data/StorableVector/Lazy.hs b/Data/StorableVector/Lazy.hs
--- a/Data/StorableVector/Lazy.hs
+++ b/Data/StorableVector/Lazy.hs
@@ -86,6 +86,11 @@
 instance Arbitrary ChunkSize where
    arbitrary = fmap (ChunkSize . max 1) arbitrary
 
+{-
+ToDo:
+Since non-negative-0.1 we have the Monoid superclass for NonNeg.
+Maybe we do not need the Num instance anymore.
+-}
 instance Num ChunkSize where
    (ChunkSize x) + (ChunkSize y)  =
        ChunkSize (x+y)
@@ -95,9 +100,13 @@
    signum  =  moduleError "ChunkSize.signum" "intentionally unimplemented"
    fromInteger = ChunkSize . fromInteger
 
+instance Monoid ChunkSize where
+   mempty = ChunkSize 0
+   mappend (ChunkSize x) (ChunkSize y) = ChunkSize (x+y)
+   mconcat = ChunkSize . sum . List.map (\(ChunkSize c) -> c)
+
 instance NonNeg.C ChunkSize where
-   (ChunkSize x) -| (ChunkSize y)  =
-      ChunkSize $ if x >= y then x-y else 0
+   split = NonNeg.splitDefault (\(ChunkSize c) -> c) ChunkSize
 
 chunkSize :: Int -> ChunkSize
 chunkSize x =
diff --git a/storablevector.cabal b/storablevector.cabal
--- a/storablevector.cabal
+++ b/storablevector.cabal
@@ -1,5 +1,5 @@
 Name:                storablevector
-Version:             0.2.6
+Version:             0.2.7
 Category:            Data
 Synopsis:            Fast, packed, strict storable arrays with a list interface like ByteString
 Description:
@@ -51,11 +51,11 @@
 Source-Repository this
   type:     darcs
   location: http://code.haskell.org/storablevector/
-  tag:      0.2.6
+  tag:      0.2.7
 
 Library
   Build-Depends:
-    non-negative >= 0.0.4 && <0.1,
+    non-negative >= 0.1 && <0.2,
     utility-ht >= 0.0.5 && <0.1,
     transformers >=0.2 && <0.3,
     QuickCheck >= 1 && < 3