diff --git a/Network/TLS/Context.hs b/Network/TLS/Context.hs
--- a/Network/TLS/Context.hs
+++ b/Network/TLS/Context.hs
@@ -56,7 +56,7 @@
 
 import Control.Concurrent.MVar
 import Control.Monad.State
-import Control.Exception (throwIO, Exception(), onException)
+import Control.Exception (throwIO, Exception())
 import Data.IORef
 import System.IO (Handle, hSetBuffering, BufferMode(..), hFlush)
 import Prelude hiding (catch)
@@ -64,8 +64,8 @@
 data TLSLogging = TLSLogging
 	{ loggingPacketSent :: String -> IO ()
 	, loggingPacketRecv :: String -> IO ()
-	, loggingIOSent     :: Bytes -> IO ()
-	, loggingIORecv     :: Header -> Bytes -> IO ()
+	, loggingIOSent     :: B.ByteString -> IO ()
+	, loggingIORecv     :: Header -> B.ByteString -> IO ()
 	}
 
 data TLSParams = TLSParams
@@ -152,7 +152,9 @@
 	}
 
 updateMeasure :: MonadIO m => TLSCtx c -> (Measurement -> Measurement) -> m ()
-updateMeasure ctx f = liftIO $ modifyIORef (ctxMeasurement ctx) f
+updateMeasure ctx f = liftIO $ do
+    x <- readIORef (ctxMeasurement ctx)
+    writeIORef (ctxMeasurement ctx) $! f x
 
 withMeasure :: MonadIO m => TLSCtx c -> (Measurement -> IO a) -> m a
 withMeasure ctx f = liftIO (readIORef (ctxMeasurement ctx) >>= f)
@@ -209,13 +211,10 @@
 
 
 usingState :: MonadIO m => TLSCtx c -> TLSSt a -> m (Either TLSError a)
-usingState ctx f = liftIO (takeMVar mvar) >>= \st -> liftIO $ onException (execAndStore st) (putMVar mvar st)
-	where
-		mvar = ctxState ctx
-		execAndStore st = do
-			let (a, newst) = runTLSState f st
-			putMVar mvar newst
-			return a
+usingState ctx f =
+	liftIO $ modifyMVar (ctxState ctx) $ \st ->
+		let (a, newst) = runTLSState f st
+		 in newst `seq` return (newst, a)
 
 usingState_ :: MonadIO m => TLSCtx c -> TLSSt a -> m a
 usingState_ ctx f = do
diff --git a/Network/TLS/Core.hs b/Network/TLS/Core.hs
--- a/Network/TLS/Core.hs
+++ b/Network/TLS/Core.hs
@@ -178,15 +178,15 @@
            -> g                 -- ^ Random number generator associated
            -> c                 -- ^ An abstract connection type
            -> IO ()             -- ^ A method for the connection buffer to be flushed
-           -> (Bytes -> IO ())  -- ^ A method for sending bytes through the connection
-           -> (Int -> IO Bytes) -- ^ A method for receiving bytes through the connection
+           -> (B.ByteString -> IO ())  -- ^ A method for sending bytes through the connection
+           -> (Int -> IO B.ByteString) -- ^ A method for receiving bytes through the connection
            -> m (TLSCtx c)
 clientWith params rng connection flushF sendF recvF =
 	liftIO $ newCtxWith connection flushF sendF recvF params st
 	where st = (newTLSState rng) { stClientContext = True }
 
 -- | Create a new Client context with a configuration, a RNG, and a Handle.
--- It reconfigures the handle buffermode to noBuffering
+-- It reconfigures the handle's 'System.IO.BufferMode' to @NoBuffering@.
 client :: (MonadIO m, CryptoRandomGen g)
        => TLSParams -- ^ parameters to use for this context
        -> g         -- ^ random number generator associated with the context
@@ -196,13 +196,13 @@
 	where st = (newTLSState rng) { stClientContext = True }
 
 -- | Create a new Server context with a configuration, a RNG, a generic connection and the connection operation.
-serverWith :: (MonadIO m, CryptoRandomGen g) => TLSParams -> g -> c -> IO () -> (Bytes -> IO ()) -> (Int -> IO Bytes) -> m (TLSCtx c)
+serverWith :: (MonadIO m, CryptoRandomGen g) => TLSParams -> g -> c -> IO () -> (B.ByteString -> IO ()) -> (Int -> IO B.ByteString) -> m (TLSCtx c)
 serverWith params rng connection flushF sendF recvF =
 	liftIO $ newCtxWith connection flushF sendF recvF params st
 	where st = (newTLSState rng) { stClientContext = False }
 
 -- | Create a new Server context with a configuration, a RNG, and a Handle.
--- It reconfigures the handle buffermode to noBuffering
+-- It reconfigures the handle's 'System.IO.BufferMode' to @NoBuffering@.
 server :: (MonadIO m, CryptoRandomGen g) => TLSParams -> g -> Handle -> m (TLSCtx Handle)
 server params rng handle = liftIO $ newCtx handle params st
 	where st = (newTLSState rng) { stClientContext = False }
@@ -477,7 +477,7 @@
 		_    -> fail ("unexpected handshake received, excepting client hello and received " ++ show hss)
 
 -- | Handshake for a new TLS connection
--- This is to be called at the beginning of a connection, and during renegociation
+-- This is to be called at the beginning of a connection, and during renegotiation
 handshake :: MonadIO m => TLSCtx c -> m ()
 handshake ctx = do
 	cc <- usingState_ ctx (stClientContext <$> get)
@@ -500,17 +500,17 @@
 			sendDataChunk remain
 		| otherwise = sendPacket ctx $ AppData d
 
--- | recvData get data out of Data packet, and automatically renegociate if
+-- | recvData get data out of Data packet, and automatically renegotiate if
 -- a Handshake ClientHello is received
-recvData :: MonadIO m => TLSCtx c -> m Bytes
+recvData :: MonadIO m => TLSCtx c -> m B.ByteString
 recvData ctx = do
 	checkValid ctx
 	pkt <- recvPacket ctx
 	case pkt of
-		-- on server context receiving a client hello == renegociation
+		-- on server context receiving a client hello == renegotiation
 		Right (Handshake [ch@(ClientHello _ _ _ _ _ _)]) ->
 			handshakeServerWith ctx ch >> recvData ctx
-		-- on client context, receiving a hello request == renegociation
+		-- on client context, receiving a hello request == renegotiation
 		Right (Handshake [HelloRequest]) ->
 			handshakeClient ctx >> recvData ctx
 		Right (Alert [(AlertLevel_Fatal, _)]) -> do
diff --git a/Network/TLS/Receiving.hs b/Network/TLS/Receiving.hs
--- a/Network/TLS/Receiving.hs
+++ b/Network/TLS/Receiving.hs
@@ -104,7 +104,7 @@
 processServerHello _ = error "processServerHello called on wrong type"
 
 -- process the client key exchange message. the protocol expects the initial
--- client version received in ClientHello, not the negociated version.
+-- client version received in ClientHello, not the negotiated version.
 -- in case the version mismatch, generate a random master secret
 processClientKeyXchg :: ByteString -> TLSSt ()
 processClientKeyXchg encryptedPremaster = do
diff --git a/tls.cabal b/tls.cabal
--- a/tls.cabal
+++ b/tls.cabal
@@ -1,5 +1,5 @@
 Name:                tls
-Version:             0.9.0
+Version:             0.9.1
 Description:
    Native Haskell TLS and SSL protocol implementation for server and client.
    .