diff --git a/LIO/TCB.hs b/LIO/TCB.hs
--- a/LIO/TCB.hs
+++ b/LIO/TCB.hs
@@ -65,6 +65,8 @@
   (LIOTCB ma) >>= k = LIOTCB $ \s -> do
     a <- ma s
     case k a of LIOTCB mb -> mb s
+
+instance MonadFail (LIO l) where
   fail = LIOTCB . const . fail
 
 instance Functor (LIO l) where
diff --git a/lio.cabal b/lio.cabal
--- a/lio.cabal
+++ b/lio.cabal
@@ -1,5 +1,5 @@
 Name:           lio
-Version:        0.11.7.0
+Version:        0.11.7.1
 Cabal-Version:  1.12
 Build-type:     Simple
 License:        MIT