diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+## 0.5.0
+
+* update `wpsProcessBody` to accept response's initial request
+
 ## 0.4.5
 
 * add `Eq, Ord, Show, Read` instances to `ProxyDest`
diff --git a/Network/HTTP/ReverseProxy.hs b/Network/HTTP/ReverseProxy.hs
--- a/Network/HTTP/ReverseProxy.hs
+++ b/Network/HTTP/ReverseProxy.hs
@@ -249,8 +249,10 @@
     -- Default: SIHFromSocket
     --
     -- Since 0.2.0
-    , wpsProcessBody :: HC.Response () -> Maybe (Conduit ByteString IO (Flush Builder))
+    , wpsProcessBody :: WAI.Request -> HC.Response () -> Maybe (Conduit ByteString IO (Flush Builder))
     -- ^ Post-process the response body returned from the host.
+    --   The API for this function changed to include the extra 'WAI.Request'
+    --   parameter in version 0.5.0.
     --
     -- Since 0.2.1
     , wpsUpgradeToRaw :: WAI.Request -> Bool
@@ -283,7 +285,7 @@
         { wpsOnExc = defaultOnExc
         , wpsTimeout = Nothing
         , wpsSetIpHeader = SIHFromSocket
-        , wpsProcessBody = const Nothing
+        , wpsProcessBody = \_ _ -> Nothing
         , wpsUpgradeToRaw = \req ->
             (CI.mk <$> lookup "upgrade" (WAI.requestHeaders req)) == Just "websocket"
         , wpsGetDest = Nothing
@@ -415,7 +417,7 @@
                     Right res -> do
                         let conduit = fromMaybe
                                         (awaitForever (\bs -> yield (Chunk $ fromByteString bs) >> yield Flush))
-                                        (wpsProcessBody wps $ const () <$> res)
+                                        (wpsProcessBody wps req $ const () <$> res)
                             src = bodyReaderSource $ HC.responseBody res
                         sendResponse $ WAI.responseStream
                             (HC.responseStatus res)
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:             0.4.5
+version:             0.5.0
 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