diff --git a/Network/Wai/Middleware/Jsonp.hs b/Network/Wai/Middleware/Jsonp.hs
--- a/Network/Wai/Middleware/Jsonp.hs
+++ b/Network/Wai/Middleware/Jsonp.hs
@@ -24,6 +24,7 @@
 import Data.Monoid (mappend)
 import Control.Monad (join)
 import Data.Maybe (fromMaybe)
+import qualified Data.ByteString as S
 
 -- | Wrap json responses in a jsonp callback.
 --
@@ -68,8 +69,9 @@
             Just _ -> addCallback c $ responseEnumerator r
             Nothing -> return r
     checkJSON hs =
-        case fmap B8.unpack $ lookup "Content-Type" hs of
-            Just "application/json" -> Just $ fixHeaders hs
+        case lookup "Content-Type" hs of
+            Just x
+                | B8.pack "application/json" `S.isPrefixOf` x -> Just $ fixHeaders hs
             _ -> Nothing
     fixHeaders = changeVal "Content-Type" "text/javascript"
     addCallback :: B8.ByteString -> (forall a. ResponseEnumerator a)
diff --git a/wai-extra.cabal b/wai-extra.cabal
--- a/wai-extra.cabal
+++ b/wai-extra.cabal
@@ -1,5 +1,5 @@
 Name:                wai-extra
-Version:             0.4.0
+Version:             0.4.0.1
 Synopsis:            Provides some basic WAI handlers and middleware.
 Description:         The goal here is to provide common features without many dependencies.
 License:             BSD3