diff --git a/Data/Graph/Wrapper.hs b/Data/Graph/Wrapper.hs
--- a/Data/Graph/Wrapper.hs
+++ b/Data/Graph/Wrapper.hs
@@ -27,7 +27,9 @@
     
     topologicalSort, depthNumbering,
     
-    SCC(..), stronglyConnectedComponents, sccGraph
+    SCC(..), stronglyConnectedComponents, sccGraph,
+    
+    traverseWithKey
   ) where
 
 import Data.Graph.Wrapper.Internal
diff --git a/Data/Graph/Wrapper/Internal.hs b/Data/Graph/Wrapper/Internal.hs
--- a/Data/Graph/Wrapper/Internal.hs
+++ b/Data/Graph/Wrapper/Internal.hs
@@ -5,6 +5,8 @@
 {-# OPTIONS_HADDOCK not-home #-}
 module Data.Graph.Wrapper.Internal where
 
+import Control.Applicative (Applicative)
+
 import Data.Array
 import Data.Maybe (fromMaybe)
 import qualified Data.Graph as G
@@ -39,6 +41,13 @@
 
 instance Traversable.Traversable (Graph i) where
     traverse f g = fmap (\gvva -> g { gVertexVertexArray = gvva }) (Traversable.traverse f (gVertexVertexArray g))
+
+
+traverseWithKey :: Applicative t => (i -> a -> t b) -> Graph i a -> t (Graph i b)
+traverseWithKey f g = fmap (\gvva -> g { gVertexVertexArray = gvva }) (traverseWithIndex (\gv -> f (gVertexIndex g gv)) (gVertexVertexArray g))
+  where
+    traverseWithIndex :: Applicative t => (G.Vertex -> a -> t b) -> Array G.Vertex a -> t (Array G.Vertex b)
+    traverseWithIndex f a = fmap (array (bounds a)) $ flip Traversable.traverse (assocs a) $ \(k, v) -> fmap ((,) k) $ f k v
 
 
 {-# RULES "indexGVertex/gVertexIndex" forall g i. gVertexIndex g (indexGVertex g i) = i #-}
diff --git a/graph-wrapper.cabal b/graph-wrapper.cabal
--- a/graph-wrapper.cabal
+++ b/graph-wrapper.cabal
@@ -1,7 +1,7 @@
 Cabal-Version:      >= 1.2
 Build-Type:         Simple
 Name:               graph-wrapper
-Version:            0.2.3
+Version:            0.2.4
 Maintainer:         Max Bolingbroke <batterseapower@hotmail.com>
 Homepage:           http://www.github.com/batterseapower/graph-wrapper
 License:            BSD3