diff --git a/Network/Wai/Handler/FastCGI.hs b/Network/Wai/Handler/FastCGI.hs
--- a/Network/Wai/Handler/FastCGI.hs
+++ b/Network/Wai/Handler/FastCGI.hs
@@ -91,8 +91,13 @@
 setHeader :: MonadFastCGI m => (W.ResponseHeader, B.ByteString) -> m ()
 setHeader (k, v) =
     setResponseHeader
-       (HttpExtensionHeader $ B.unpack $ W.responseHeaderToBS k)
+       k'
        (B.unpack v)
+  where
+    k'
+      | k == W.ContentType = HttpContentType -- avoid double-sent c-type
+      | otherwise = HttpExtensionHeader $ B.unpack $ W.responseHeaderToBS k
+
 
 myPut :: FastCGIState -> () -> B.ByteString -> IO (Either () ())
 myPut state _ bs = do
diff --git a/wai-handler-fastcgi.cabal b/wai-handler-fastcgi.cabal
--- a/wai-handler-fastcgi.cabal
+++ b/wai-handler-fastcgi.cabal
@@ -1,5 +1,5 @@
 name:            wai-handler-fastcgi
-version:         0.0.0
+version:         0.0.0.1
 license:         BSD3
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>