diff --git a/MemoTrie.cabal b/MemoTrie.cabal
--- a/MemoTrie.cabal
+++ b/MemoTrie.cabal
@@ -1,5 +1,5 @@
 Name:                MemoTrie
-Version:             0.4.11
+Version:             0.4.12
 Cabal-Version:       >= 1.2
 Synopsis:            Trie-based memo functions
 Category:            Data
@@ -24,7 +24,7 @@
 Library
   hs-Source-Dirs:      src
   Extensions:          
-  Build-Depends:       base < 5
+  Build-Depends:       base < 5, void
   Exposed-Modules:     
                      Data.MemoTrie
   ghc-options:         -Wall
diff --git a/src/Data/MemoTrie.hs b/src/Data/MemoTrie.hs
--- a/src/Data/MemoTrie.hs
+++ b/src/Data/MemoTrie.hs
@@ -32,6 +32,8 @@
 import Data.Monoid
 import Data.Function (on)
 
+import Data.Void
+
 -- import Prelude hiding (id,(.))
 -- import Control.Category
 -- import Control.Arrow
@@ -138,6 +140,13 @@
 
 
 ---- Instances
+
+instance HasTrie Void where
+  -- As suggested by Audun
+  data Void :->: a = VoidTrie 
+  trie _ = VoidTrie
+  untrie VoidTrie = absurd
+  enumerate VoidTrie = []
 
 instance HasTrie () where
     newtype () :->: a = UnitTrie a