diff --git a/Control/Concurrent/Chan/Synchronous.hs b/Control/Concurrent/Chan/Synchronous.hs
--- a/Control/Concurrent/Chan/Synchronous.hs
+++ b/Control/Concurrent/Chan/Synchronous.hs
@@ -20,7 +20,7 @@
 --
 --   [Synchronous, non-blocking] These operations complete immediately
 --     if another thread is ready to synchronize, and otherwise return
---     a failure code immediate.
+--     a failure code immediately.
 --
 --   [Asynchronous] These operations complete immediately and always
 --     succeed, though the value they send may not be received until
@@ -195,7 +195,7 @@
 getWriters (WQ q) = dequeue empty q
 
 clear :: IO a -> IORef (Maybe b) -> IO a
-clear io r = block $ io `finally` writeIORef r Nothing
+clear io r = uninterruptibleMask_ $ io `finally` writeIORef r Nothing
 
 -- | Make a new channel.
 newChan :: IO (Chan a)
@@ -341,7 +341,7 @@
       NoQ readers -> do
         message <- newEmptyMVar
         r       <- newIORef (Just message)
-        commit (RQ (readers |> r))
+        commit (RQ (readers |> r)) :: IO ()
         return $ do
           a <- takeMVar message `clear` r
           -- Race condition here!  I think we'd need a different
@@ -354,7 +354,7 @@
           Just a  -> do
             r'       <- newIORef (Just a')
             confirm' <- newEmptyMVar
-            block $ do
+            uninterruptibleMask_ $ do
               putMVar confirm ()
               commit (WQ ((r', confirm') <| writers))
             return $ do
@@ -584,7 +584,7 @@
     loop []     e = return (e, Success (Success (), []))
     loop (a:as) e = do
       case getReaders e of
-        r :< readers -> block $ do
+        r :< readers -> uninterruptibleMask_ $ do
           maybereader <- readIORef r
           case maybereader of
             Just reader -> do
@@ -608,17 +608,9 @@
 --- Helpful MVar stuff
 ---
 
-saveBlock :: IO (IO a -> IO a)
-saveBlock  = do
-  b <- blocked
-  case b of
-    True  -> return block
-    False -> return unblock
-
 modifyMVar :: MVar a -> (a -> IO (a, b)) -> IO b
-modifyMVar m io = do
-  restore <- saveBlock
-  block $ do
+modifyMVar m io =
+  uninterruptibleMask $ \restore -> do
     a <- takeMVar m
     (a',b) <- restore (io a)
       `onException` putMVar m a
@@ -628,9 +620,8 @@
 -- Control.Concurrent.MVar doesn't have this, but it's pretty useful
 -- for implementing non-blocking operations.
 tryModifyMVar :: MVar a -> (a -> IO (a, TryResult b)) -> IO (TryResult b)
-tryModifyMVar m io = do
-  restore <- saveBlock
-  block $ do
+tryModifyMVar m io =
+  uninterruptibleMask $ \restore -> do
     maybea <- tryTakeMVar m
     case maybea of
       Just a -> do
@@ -644,9 +635,8 @@
 transactMVar :: MVar a ->
                 (a -> (a -> IO ()) -> IO b) ->
                 IO b
-transactMVar m io = do
-  restore <- saveBlock
-  block $ do
+transactMVar m io =
+  uninterruptibleMask $ \restore -> do
     a <- takeMVar m
     r <- newIORef a
     restore (io a (writeIORef r))
@@ -656,9 +646,8 @@
 tryTransactMVar :: MVar a ->
                    (a -> (a -> IO ()) -> IO (TryResult b)) ->
                    IO (TryResult b)
-tryTransactMVar m io = do
-  restore <- saveBlock
-  block $ do
+tryTransactMVar m io =
+  uninterruptibleMask $ \restore -> do
     maybea <- tryTakeMVar m
     case maybea of
       Just a -> do
diff --git a/synchronous-channels.cabal b/synchronous-channels.cabal
--- a/synchronous-channels.cabal
+++ b/synchronous-channels.cabal
@@ -1,5 +1,5 @@
 Name:           synchronous-channels
-Version:        0.1
+Version:        0.2
 Cabal-Version:  >= 1.2.3
 License:        BSD3
 License-File:   LICENSE
@@ -9,14 +9,14 @@
 Category:       Concurrency, Control
 Synopsis:       Synchronous communication channels
 Build-type:     Simple
-Tested-with:    GHC == 6.10.1
+Tested-with:    GHC == 7.8.3
 Description:
         Synchronous communication channels.  These are similar to
         'Control.Concurrent.Chan.Chan',
         but a writer blocks until it can synchronize with a reader.
 
 Library
-  Build-Depends:        base >= 4
+  Build-Depends:        base >= 4 && < 5
   GHC-Options:          -W -Wall
 
   Exposed-modules: