diff --git a/Control/Monad/SearchTree.hs b/Control/Monad/SearchTree.hs
--- a/Control/Monad/SearchTree.hs
+++ b/Control/Monad/SearchTree.hs
@@ -61,6 +61,7 @@
  where
   return x = Search ($x)
   a >>= f  = Search (\k -> search a (\x -> search (f x) k))
+  fail _   = mzero
 
 instance MonadPlus Search
  where
diff --git a/tree-monad.cabal b/tree-monad.cabal
--- a/tree-monad.cabal
+++ b/tree-monad.cabal
@@ -1,5 +1,5 @@
 Name:          tree-monad
-Version:       0.2
+Version:       0.2.1
 Cabal-Version: >= 1.6
 Synopsis:      Non-Determinism Monad for Tree Search
 Description: