diff --git a/Data/Conduit/Process.hs b/Data/Conduit/Process.hs
--- a/Data/Conduit/Process.hs
+++ b/Data/Conduit/Process.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE FlexibleContexts, OverloadedStrings, DoAndIfThenElse #-}
+{-# LANGUAGE FlexibleContexts, OverloadedStrings, DoAndIfThenElse, BangPatterns #-}
 module Data.Conduit.Process (
   -- * Run process
   pipeProcess,
@@ -19,6 +19,8 @@
   ProcessHandle,
   ) where
 
+import Control.Concurrent
+import Control.Concurrent.MVar
 import Control.Monad
 import Control.Monad.Trans
 import Control.Monad.Trans.Resource
@@ -39,7 +41,8 @@
      -> Pipe B.ByteString B.ByteString m ()
 pipeProcess cp = flip PipeM (return ()) $ do
   (_, (Just cin, Just cout, _, ph)) <- allocate createp closep
-  return $ go cin cout ph B.hGetNonBlocking
+  mvar <- liftIO newEmptyMVar
+  return $ go cin cout ph mvar False B.hGetNonBlocking
   where
     createp = createProcess cp
       { std_in  = CreatePipe
@@ -52,7 +55,7 @@
       _ <- waitForProcess ph
       return ()
 
-    go cin cout ph rd = do
+    go !cin !cout !ph !mvar !wait !rd = do
       out <- liftIO $ rd cout bufSize
       if B.null out then do
         end <- liftIO $ getProcessExitCode ph
@@ -60,15 +63,25 @@
           Just ec -> do
             lift $ when (ec /= ExitSuccess) $ monadThrow ec
             Done Nothing ()
-          Nothing -> do
-            NeedInput
-              (\inp -> do
-                  liftIO $ B.hPut cin inp >> hFlush cin
-                  go cin cout ph rd)
-              (do liftIO (hClose cin)
-                  go cin cout ph B.hGetSome)
+          Nothing ->
+            if wait then do
+              emp <- liftIO $ isEmptyMVar mvar
+              if emp then do
+                go cin cout ph mvar wait rd
+              else do
+                liftIO $ takeMVar mvar
+                go cin cout ph mvar False rd
+            else do
+              NeedInput
+                (\inp -> do
+                    liftIO $ do
+                      B.hPut cin inp
+                      forkIO (hFlush cin >>= putMVar mvar)
+                    go cin cout ph mvar True rd)
+                (do liftIO (hClose cin)
+                    go cin cout ph mvar wait B.hGetSome)
       else do
-        HaveOutput (go cin cout ph rd) (return ()) out
+        HaveOutput (go cin cout ph mvar wait rd) (return ()) out
 
 -- | Source of process
 sourceProcess :: MonadResource m => CreateProcess -> Source m B.ByteString
diff --git a/process-conduit.cabal b/process-conduit.cabal
--- a/process-conduit.cabal
+++ b/process-conduit.cabal
@@ -1,5 +1,5 @@
 Name:                process-conduit
-Version:             0.4.0
+Version:             0.4.1
 Synopsis:            Conduits for processes
 
 Description:
@@ -32,7 +32,7 @@
   
   Build-depends:       base             == 4.*
                      , template-haskell >= 2.4 && < 2.8
-                     , mtl              == 2.0.*
+                     , mtl              >= 2.0 && < 2.2
                      , bytestring       == 0.9.*
                      , text             == 0.11.*
                      , process          >= 1.0 && < 1.2
@@ -46,7 +46,7 @@
   Hs-source-dirs:      examples
   Main-is:             TestConduit.hs
   Build-depends:       base            == 4.*
-                     , conduit         == 0.4.*
+                     , conduit
                      , process-conduit
   if !flag(examples)
     Buildable:         False