diff --git a/mstate.cabal b/mstate.cabal
--- a/mstate.cabal
+++ b/mstate.cabal
@@ -8,13 +8,17 @@
 Author:         Nils Schweinsberg
 Maintainer:     <mail@nils.cc>
 
-Version:        0.2.7
+Version:        0.2.8
 Category:       Concurrency, Monads
 License:        BSD3
 License-File:   LICENSE
 Cabal-Version:  >= 1.6
 Build-Type:     Simple
 
+source-repository head
+  type:         git
+  location:     https://github.com/nilscc/mstate
+
 Library
     GHC-Options:        -Wall
     Hs-Source-Dirs:     src
@@ -22,7 +26,8 @@
         base       == 4.*,
         mtl,
         stm,
-        monad-peel >= 0.1.1
+        monad-peel >= 0.1.1,
+        fail
 
     Exposed-Modules:
         Control.Concurrent.MState
diff --git a/src/Control/Concurrent/MState.hs b/src/Control/Concurrent/MState.hs
--- a/src/Control/Concurrent/MState.hs
+++ b/src/Control/Concurrent/MState.hs
@@ -42,7 +42,8 @@
 import Control.Applicative
 import Control.Monad.State.Class
 import Control.Monad.Cont
-import Control.Monad.Error
+import Control.Monad.Except
+import qualified Control.Monad.Fail as Fail
 import Control.Monad.Reader
 import Control.Monad.Writer
 
@@ -72,8 +73,10 @@
           -> t                 -- ^ Initial state value
           -> m (a,t)
 runMState m t = do
-  (a, Just t') <- runAndWaitMaybe True m t
-  return (a, t')
+  (a, t') <- runAndWaitMaybe True m t
+  case t' of
+      Just t'' -> return (a, t'')
+      _ -> undefined  -- impossible
 
 runAndWaitMaybe :: MonadPeelIO m
                 => Bool
@@ -130,7 +133,7 @@
     liftIO . atomically $ writeTVar r v'
     return b
 
-mapMState_ :: (MonadIO m, MonadIO n)
+mapMState_ :: (MonadIO n)
            => (m a -> n b)
            -> MState t m a
            -> MState t n b
@@ -221,12 +224,14 @@
 -- Monad instances
 --------------------------------------------------------------------------------
 
+instance (Fail.MonadFail m) => Fail.MonadFail (MState t m) where
+    fail str = MState $ \_ -> Fail.fail str
+
 instance (Monad m) => Monad (MState t m) where
     return a = MState $ \_ -> return a
     m >>= k  = MState $ \t -> do
         a <- runMState' m t
         runMState' (k a) t
-    fail str = MState $ \_ -> fail str
 
 instance (Functor f) => Functor (MState t f) where
     fmap f m = MState $ \t -> fmap f (runMState' m t)