diff --git a/comfort-graph.cabal b/comfort-graph.cabal
--- a/comfort-graph.cabal
+++ b/comfort-graph.cabal
@@ -1,5 +1,5 @@
 Name:                comfort-graph
-Version:             0.0.2
+Version:             0.0.2.1
 Synopsis:            Graph structure with type parameters for nodes and edges
 Description:
   This graph structure is based on "Data.Map"
@@ -51,7 +51,7 @@
 Cabal-Version:       >=1.10
 
 Source-Repository this
-  Tag:         0.0.2
+  Tag:         0.0.2.1
   Type:        darcs
   Location:    http://hub.darcs.net/thielema/comfort-graph
 
diff --git a/src/Data/Graph/Comfort/Map.hs b/src/Data/Graph/Comfort/Map.hs
--- a/src/Data/Graph/Comfort/Map.hs
+++ b/src/Data/Graph/Comfort/Map.hs
@@ -87,13 +87,7 @@
    Map k0 (Map k1 a) -> Map k1 (Map k0 a)
 flip =
    Map.unionsWith (Map.unionWith (error $ "Map.flip: duplicate key")) .
-   concat .
-   Map.elems .
-   Map.mapWithKey
-      (\k0 ->
-         Map.elems .
-         Map.mapWithKey
-            (\k1 a -> Map.singleton k1 $ Map.singleton k0 a))
+   Map.elems . Map.mapWithKey (fmap . Map.singleton)
 
 
 mapMaybeKeys ::