diff --git a/Network/HTTP/ReverseProxy.hs b/Network/HTTP/ReverseProxy.hs
--- a/Network/HTTP/ReverseProxy.hs
+++ b/Network/HTTP/ReverseProxy.hs
@@ -146,7 +146,7 @@
                     , HC.path = WAI.rawPathInfo req
                     , HC.queryString = WAI.rawQueryString req
                     , HC.requestHeaders = filter (\(key, _) -> not $ key `member` strippedHeaders) $ WAI.requestHeaders req
-                    , HC.requestBody = HC.RequestBodySourceChunked $ mapOutput fromByteString $ WAI.requestBody req
+                    , HC.requestBody = body
                     , HC.redirectCount = 0
 #if MIN_VERSION_http_conduit(1, 9, 0)
                     , HC.checkStatus = \_ _ _ -> Nothing
@@ -155,6 +155,18 @@
 #endif
                     , HC.responseTimeout = wpsTimeout wps
                     }
+                bodySrc = mapOutput fromByteString $ WAI.requestBody req
+                bodyChunked = HC.RequestBodySourceChunked bodySrc
+#if MIN_VERSION_wai(1, 4, 0)
+                body =
+                    case WAI.requestBodyLength req of
+                        WAI.KnownLength i -> HC.RequestBodySource
+                            (fromIntegral i)
+                            bodySrc
+                        WAI.ChunkedBody -> bodyChunked
+#else
+                body = bodyChunked
+#endif
             ex <- try $ HC.http req' manager
             case ex of
                 Left e -> wpsOnExc wps e req
@@ -162,8 +174,9 @@
                     (src, _) <- unwrapResumable $ HC.responseBody res
                     return $ WAI.ResponseSource
                         (HC.responseStatus res)
-                        (filter (\(key, _) -> not $ key `member` strippedHeaders) $ HC.responseHeaders res)
-                        (src =$= awaitForever (\bs -> yield (Chunk $ fromByteString bs) >> yield Flush))
+                        (filter (\(key, _) -> not $ key `member` strippedHeaders) $ HC.responseHeaders res) $ do
+                        yield Flush
+                        src =$= awaitForever (\bs -> yield (Chunk $ fromByteString bs) >> yield Flush)
   where
     strippedHeaders = asSet $ fromList ["content-length", "transfer-encoding", "accept-encoding", "content-encoding"]
     asSet :: Set a -> Set a
diff --git a/http-reverse-proxy.cabal b/http-reverse-proxy.cabal
--- a/http-reverse-proxy.cabal
+++ b/http-reverse-proxy.cabal
@@ -1,5 +1,5 @@
 name:                http-reverse-proxy
-version:             0.1.1.4
+version:             0.1.1.5
 synopsis:            Reverse proxy HTTP requests, either over raw sockets or with WAI
 description:         Provides a simple means of reverse-proxying HTTP requests. The raw approach uses the same technique as leveraged by keter, whereas the WAI approach performs full request/response parsing via WAI and http-conduit.
 homepage:            https://github.com/fpco/http-reverse-proxy
diff --git a/test/main.hs b/test/main.hs
--- a/test/main.hs
+++ b/test/main.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                 #-}
 {-# LANGUAGE OverloadedStrings   #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 import           Blaze.ByteString.Builder   (fromByteString)
@@ -7,6 +8,8 @@
                                              try)
 import           Control.Monad              (forever)
 import           Control.Monad.IO.Class     (liftIO)
+import qualified Data.ByteString            as S
+import qualified Data.ByteString.Char8      as S8
 import qualified Data.ByteString.Lazy.Char8 as L8
 import           Data.Conduit               (Flush (..), await, runResourceT,
                                              yield, ($$+-))
@@ -95,6 +98,30 @@
                         res <- HC.http req manager
                         HC.responseBody res $$+- await
                     mbs `shouldBe` Just (Just "hello")
+#if MIN_VERSION_wai(1, 4, 0)
+        it "passes on body length" $
+            let app req = return $ responseLBS
+                    status200
+                    [("uplength", show' $ Network.Wai.requestBodyLength req)]
+                    ""
+                body = "some body"
+                show' Network.Wai.ChunkedBody = "chunked"
+                show' (Network.Wai.KnownLength i) = S8.pack $ show i
+             in withMan $ \manager ->
+                withWApp app $ \port1 ->
+                withWApp (waiProxyTo (const $ return $ Right $ ProxyDest "127.0.0.1" port1) defaultOnExc manager) $ \port2 -> do
+                    req' <- HC.parseUrl $ "http://127.0.0.1:" ++ show port2
+                    let req = req'
+                            { HC.requestBody = HC.RequestBodyBS body
+                            }
+                    mlen <- runResourceT $ do
+                        res <- HC.http req manager
+                        return $ lookup "uplength" $ HC.responseHeaders res
+                    mlen `shouldBe` Just (show'
+                                            $ Network.Wai.KnownLength
+                                            $ fromIntegral
+                                            $ S.length body)
+#endif
     describe "waiToRaw" $ do
         it "works" $ do
             let content = "waiToRaw"