diff --git a/Network/Wai/Application/Classic/RevProxy.hs b/Network/Wai/Application/Classic/RevProxy.hs
--- a/Network/Wai/Application/Classic/RevProxy.hs
+++ b/Network/Wai/Application/Classic/RevProxy.hs
@@ -75,7 +75,7 @@
     hdr = requestHeaders req
     query = rawQueryString req
     len = requestBodyLength req
-    body = requestBody req
+    body = getRequestBodyChunk req
     path' = dst </> (path <\> src)
     dropQuestion q = case BS.uncons q of
         Just (63, q') -> q' -- '?' is 63
diff --git a/wai-app-file-cgi.cabal b/wai-app-file-cgi.cabal
--- a/wai-app-file-cgi.cabal
+++ b/wai-app-file-cgi.cabal
@@ -1,5 +1,5 @@
 Name:                   wai-app-file-cgi
-Version:                3.1.9
+Version:                3.1.10
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3
@@ -75,7 +75,7 @@
   HS-Source-Dirs:       test
   Ghc-Options:          -threaded -Wall
   Main-Is:              doctests.hs
-  Build-Depends:        base
+  Build-Depends:        base >= 4.9 && < 5
                       , doctest >= 0.9.3
   if impl(ghc >= 8)
     Default-Extensions:  Strict StrictData
@@ -87,7 +87,7 @@
   Ghc-Options:          -threaded -Wall
   Main-Is:              Spec.hs
   Other-Modules:        ClassicSpec
-  Build-Depends:        base
+  Build-Depends:        base >= 4.9 && < 5
                       , bytestring
                       , conduit >= 1.1
                       , conduit-extra