diff --git a/Network/Wai/Handler/Warp.hs b/Network/Wai/Handler/Warp.hs
--- a/Network/Wai/Handler/Warp.hs
+++ b/Network/Wai/Handler/Warp.hs
@@ -39,6 +39,7 @@
     , InvalidRequest (..)
 #if TEST
     , takeHeaders
+    , readInt
 #endif
     ) where
 
@@ -62,7 +63,7 @@
     ( bracket, finally, Exception, SomeException, catch
     , fromException
     )
-import Control.Concurrent (forkIO, threadWaitWrite)
+import Control.Concurrent (forkIO)
 import qualified Data.Char as C
 import Data.Maybe (fromMaybe)
 
@@ -79,8 +80,10 @@
     (copyByteString, Builder, toLazyByteString, toByteStringIO)
 import Blaze.ByteString.Builder.Char8 (fromChar, fromShow)
 import Data.Monoid (mappend, mconcat)
-import Network.Socket.SendFile (sendFileIterWith,sendFileIterWith', Iter (..))
+import Network.Sendfile
 
+import qualified System.PosixCompat.Files as P
+
 import Control.Monad.IO.Class (liftIO)
 import qualified Timeout as T
 import Data.Word (Word8)
@@ -183,9 +186,6 @@
 bytesPerRead = 4096
 maxTotalHeaderLength = 50 * 1024
 
-sendFileCount :: Integer
-sendFileCount = 65536
-
 data InvalidRequest =
     NotEnoughLines [String]
     | BadFirstLine String
@@ -299,27 +299,30 @@
 sendResponse :: T.Handle
              -> Request -> H.HttpVersion -> Socket -> Response -> IO Bool
 sendResponse th req hv socket (ResponseFile s hs fp mpart) = do
-    Sock.sendMany socket $ L.toChunks $ toLazyByteString $ headers hv s hs False
+    (hs', cl) <-
+        case (readInt `fmap` lookup "content-length" hs, mpart) of
+            (Just cl, _) -> return (hs, cl)
+            (Nothing, Nothing) -> do
+                cl <- P.fileSize `fmap` P.getFileStatus fp
+                return (("Content-Length", B.pack $ show cl):hs, fromIntegral cl)
+            (Nothing, Just part) -> do
+                let cl = filePartByteCount part
+                return (("Content-Length", B.pack $ show cl):hs, fromIntegral cl)
+    Sock.sendMany socket $ L.toChunks $ toLazyByteString $ headers hv s hs' False
     if hasBody s req
         then do
             case mpart of
-                Nothing -> sendFileIterWith tickler socket fp sendFileCount
-                Just part ->
-                    sendFileIterWith' tickler socket fp sendFileCount
-                        (filePartOffset part)
-                        (filePartByteCount part)
-            return $ lookup "content-length" hs /= Nothing
+                Nothing   -> sendfile socket fp PartOfFile {
+                    rangeOffset = 0
+                  , rangeLength = cl
+                  } (T.tickle th)
+                Just part -> sendfile socket fp PartOfFile {
+                    rangeOffset = filePartOffset part
+                  , rangeLength = filePartByteCount part
+                  } (T.tickle th)
+            T.tickle th
+            return True
         else return True
-  where
-    tickler iter = do
-        r <- iter
-        case r of
-            Done _ -> return ()
-            Sent _ cont -> T.tickle th >> tickler cont
-            WouldBlock _ fd cont -> do
-                -- FIXME do we want to tickle here?
-                threadWaitWrite fd
-                tickler cont
 sendResponse th req hv socket (ResponseBuilder s hs b)
     | hasBody s req = do
           toByteStringIO (\bs -> do
@@ -509,3 +512,8 @@
         then p
         else pos
 {-# INLINE checkCR #-}
+
+-- Note: This function produces garbage on invalid input. But serving an
+-- invalid content-length is a bad idea, mkay?
+readInt :: S.ByteString -> Integer
+readInt = S.foldl' (\x w -> x * 10 + fromIntegral w - 48) 0
diff --git a/warp.cabal b/warp.cabal
--- a/warp.cabal
+++ b/warp.cabal
@@ -1,5 +1,5 @@
 Name:                warp
-Version:             0.4.0.1
+Version:             0.4.1
 Synopsis:            A fast, light-weight web server for WAI applications.
 License:             BSD3
 License-file:        LICENSE
@@ -22,9 +22,10 @@
                    , transformers                  >= 0.2      && < 0.3
                    , enumerator                    >= 0.4.5    && < 0.5
                    , blaze-builder                 >= 0.2.1.4  && < 0.4
-                   , sendfile                      >= 0.7.2    && < 0.8
+                   , simple-sendfile               >= 0.1      && < 0.2
                    , http-types                    >= 0.6      && < 0.7
                    , case-insensitive              >= 0.2      && < 0.3
+                   , unix-compat                   >= 0.2      && < 0.3
   if flag(network-bytestring)
       build-depends: network               >= 2.2.1   && < 2.2.3
                    , network-bytestring    >= 0.1.3   && < 0.1.4