diff --git a/Data/Key.hs b/Data/Key.hs
--- a/Data/Key.hs
+++ b/Data/Key.hs
@@ -516,12 +516,12 @@
 instance Keyed [] where
   mapWithKey f xs0 = go xs0 0 where
     go [] _ = []
-    go (x:xs) n = f n x : (go xs $! n)
+    go (x:xs) n = f n x : (go xs $! (n + 1))
 
 instance FoldableWithKey [] where
   foldrWithKey f z0 xs0 = go z0 xs0 0 where
     go z [] _ = z
-    go z (x:xs) n = f n x (go z xs $! n)
+    go z (x:xs) n = f n x (go z xs $! (n + 1))
 
 instance TraversableWithKey [] where
   traverseWithKey f xs0 = go xs0 0 where
diff --git a/keys.cabal b/keys.cabal
--- a/keys.cabal
+++ b/keys.cabal
@@ -1,6 +1,6 @@
 name:          keys
 category:      Data Structures, Containers
-version:       0.2.6
+version:       0.2.7
 license:       BSD3
 cabal-version: >= 1.6
 license-file:  LICENSE