diff --git a/atrans.cabal b/atrans.cabal
--- a/atrans.cabal
+++ b/atrans.cabal
@@ -1,5 +1,5 @@
 name:                atrans
-version:             0.1.0.0
+version:             0.1.0.1
 synopsis:            A small collection of monad (transformer) instances.
 description:         Defines monad transformers and gives instances based on the mtl transformer library.
 homepage:            https://github.com/aphorisme/atrans
diff --git a/src/Control/Monad/Backend.hs b/src/Control/Monad/Backend.hs
--- a/src/Control/Monad/Backend.hs
+++ b/src/Control/Monad/Backend.hs
@@ -16,11 +16,11 @@
 
 import Control.Monad.Except
 import Control.Monad.State
-import Control.Concurrent.MVar (MVar, isEmptyMVar, takeMVar, putMVar, readMVar)
+import Control.Concurrent.MVar (MVar, isEmptyMVar, modifyMVar_, takeMVar, putMVar, readMVar)
 import Control.Arrow (second)
 
 
--- | The 'BackendT' transformer is a 'StateT', where the state is encapsulated into a 'MVar'.
+-- | The 'BackendT' transformer is a 'StateT', where the state is encapsulated into a 'MVar'. The initialized 'MVar' has to be non empty, otherwise every state change is blocking.
 newtype BackendT s m a = BackendT (MVar s -> m (MVar s, a))
 
 -- | 'runBackendT' unwraps the 'BackendT' monad.
@@ -41,9 +41,12 @@
 instance (Monad m, MonadIO m) => MonadState s (BackendT s m) where
   get = BackendT $ \s -> do { v <- liftIO (readMVar s); return (s, v) }
   put s = BackendT $
-    \st -> do b <- liftIO (isEmptyMVar st)
-              if b then do { liftIO (putMVar st s); return (st, ()) }
-              else do { liftIO (takeMVar st); liftIO (putMVar st s); return (st, ()) }
+    \st -> do { liftIO (modifyMVar_ st (\_ -> return s)); return (st, ()) }
+  state f = BackendT $
+    \ms -> do s <- liftIO (takeMVar ms)
+              let (x, s') = f s
+              liftIO (putMVar ms s')
+              return (ms, x)
 
 instance (Monad m, MonadIO m) => MonadIO (BackendT s m) where
   liftIO io = BackendT $ \s -> do { x <- liftIO io; return (s, x) }