diff --git a/Network/Wai/Handler/Warp/Response.hs b/Network/Wai/Handler/Warp/Response.hs
--- a/Network/Wai/Handler/Warp/Response.hs
+++ b/Network/Wai/Handler/Warp/Response.hs
@@ -57,28 +57,35 @@
 -- $setup
 -- >>> :set -XOverloadedStrings
 
+mapRight :: (b -> c) -> Either a b -> Either a c
+mapRight f eith = case eith of
+    Right x -> Right (f x)
+    Left l -> Left l
+
 ----------------------------------------------------------------
 
 fileRange :: H.Status -> H.ResponseHeaders -> FilePath
            -> Maybe FilePart -> Maybe HeaderValue
-          -> IO (Either SomeException
+          -> IO (Either IOException
                         (H.Status, H.ResponseHeaders, Integer, Integer))
-fileRange s0 hs0 path mPart mRange = try $ do
-    fileSize <- checkFileSize mPart
-    let (beg, end, len, isEntire) = checkPartRange fileSize mPart mRange
-    let hs1 = addContentLength len hs0
-        hs | isEntire  = hs1
-           | otherwise = addContentRange beg end fileSize hs1
-        s  | isEntire  = s0
-           | otherwise = H.status206
-    return (s, hs, beg, len)
+fileRange s0 hs0 path mPart mRange =
+    mapRight (fileRangeSized . fromIntegral . P.fileSize) <$>
+        try (P.getFileStatus path)
  where
-    checkFileSize Nothing = fromIntegral . P.fileSize <$> P.getFileStatus path
-    checkFileSize (Just part) = return $ filePartFileSize part
+    fileRangeSized :: Integer -> (H.Status, H.ResponseHeaders, Integer, Integer)
+    fileRangeSized fileSize =
+        let (beg, end, len, isEntire) = checkPartRange fileSize mPart mRange
+            hs1 = addContentLength len hs0
+            hs | isEntire  = hs1
+               | otherwise = addContentRange beg end fileSize hs1
+            s  | isEntire  = s0
+               | otherwise = H.status206
+        in  (s, hs, beg, len)
 
+
 checkPartRange :: Integer -> Maybe FilePart -> Maybe HeaderValue
                -> (Integer, Integer, Integer, Bool)
-checkPartRange fileSize mPart mRange = checkPart mPart mRange
+checkPartRange fileSize = checkPart
   where
     checkPart Nothing Nothing = (0, fileSize - 1, fileSize, True)
     checkPart Nothing (Just range) = case parseByteRanges range >>= listToMaybe of
@@ -184,10 +191,10 @@
         ResponseSource _ _ fb       -> RspSource fb needsChunked th
         ResponseRaw raw _           -> RspRaw raw leftover' (T.tickle th)
     ret = case response of
-        ResponseFile _ _ _ _  -> isPersist
-        ResponseBuilder _ _ _ -> isKeepAlive
-        ResponseSource _ _ _  -> isKeepAlive
-        ResponseRaw _ _       -> False
+        ResponseFile    {} -> isPersist
+        ResponseBuilder {} -> isKeepAlive
+        ResponseSource  {} -> isKeepAlive
+        ResponseRaw     {} -> False
 
 ----------------------------------------------------------------
 
@@ -208,7 +215,11 @@
 sendRsp conn ver s0 hs0 restore (RspFile path mPart mRange hook) = restore $ do
     ex <- fileRange s0 hs path mPart mRange
     case ex of
-        Left _ -> sendRsp conn ver s2 hs2 id (RspBuilder body True)
+        Left _ex ->
+#ifdef WARP_DEBUG
+          print _ex >>
+#endif
+          sendRsp conn ver s2 hs2 id (RspBuilder body True)
         Right (s, hs1, beg, len) -> do
             lheader <- composeHeader ver s hs1
             connSendFile conn path beg len hook [lheader]
diff --git a/warp.cabal b/warp.cabal
--- a/warp.cabal
+++ b/warp.cabal
@@ -1,5 +1,5 @@
 Name:                warp
-Version:             2.1.4
+Version:             2.1.4.1
 Synopsis:            A fast, light-weight web server for WAI applications.
 License:             MIT
 License-file:        LICENSE
@@ -31,6 +31,10 @@
     Description: Allow use of sendfileFd (not available on GNU/kFreeBSD)
     Default:     True
 
+Flag warp-debug
+    Description: print debug output. not suitable for production
+    Default:     False
+
 Library
   Build-Depends:     base                      >= 3        && < 5
                    , array
@@ -79,6 +83,9 @@
                      Network.Wai.Handler.Warp.Types
                      Paths_warp
   Ghc-Options:       -Wall
+
+  if flag(warp-debug)
+      Cpp-Options:   -DWARP_DEBUG
   if (os(linux) || os(freebsd) || os(darwin)) && flag(allow-sendfilefd)
       Cpp-Options:   -DSENDFILEFD
       Build-Depends: hashable