diff --git a/src/Network/Wai/Middleware/ContentType.hs b/src/Network/Wai/Middleware/ContentType.hs
--- a/src/Network/Wai/Middleware/ContentType.hs
+++ b/src/Network/Wai/Middleware/ContentType.hs
@@ -46,6 +46,7 @@
 import Network.Wai.Trans (Response, MiddlewareT, requestHeaders,
                          pathInfo)
 import qualified Data.HashMap.Lazy as HM
+import qualified Data.HashSet  as HS
 import Data.Monoid
 import Control.Monad
 
@@ -61,13 +62,14 @@
     getFirst
   . foldMap (\fe -> First $ runResponseVia <$> HM.lookup fe m)
   . findFE
-  $ maybe (HM.keys m) possibleFileExts mAcceptBS
+  $ maybe (HM.keys m) (possibleFileExts $ HM.keys m) mAcceptBS
   where
     findFE :: [FileExt] -> [FileExt]
     findFE xs =
       case mFe of
         Nothing -> xs
-        Just fe -> fe <$ guard (fe `elem` xs)
+        Just fe | fe `elem` xs -> [fe]
+                | otherwise    -> []
 
 
 fileExtsToMiddleware :: Monad m => FileExtListenerT m a -> MiddlewareT m
diff --git a/src/Network/Wai/Middleware/ContentType/Types.hs b/src/Network/Wai/Middleware/ContentType/Types.hs
--- a/src/Network/Wai/Middleware/ContentType/Types.hs
+++ b/src/Network/Wai/Middleware/ContentType/Types.hs
@@ -25,7 +25,6 @@
 module Network.Wai.Middleware.ContentType.Types
   ( -- * Types
     FileExt (..)
-  , allFileExts
   , getFileExt
   , toExt
   , ResponseVia (..)
@@ -48,7 +47,7 @@
 import           Data.HashMap.Lazy hiding (null)
 import qualified Data.HashMap.Lazy as HM
 import           Data.Monoid
-import           Data.Maybe (fromMaybe, catMaybes)
+import           Data.Maybe (fromMaybe)
 import           Data.Url
 import           Data.Hashable
 import qualified Data.ByteString        as BS
@@ -90,12 +89,7 @@
 
 instance Hashable FileExt
 
--- | All file extensions, in the order of likeliness
-allFileExts :: [FileExt]
-allFileExts = [Html,Text,Json,JavaScript,Css,Markdown]
 
-{-# INLINEABLE allFileExts #-}
-
 -- | Gets the known file extension from a Request's 'Network.Wai.pathInfo'.
 getFileExt :: [T.Text] -> Maybe FileExt
 getFileExt chunks = case chunks of
@@ -108,7 +102,7 @@
 --   to a known one.
 toExt :: (T.Text, T.Text) -> Maybe FileExt
 toExt (y,x)
-  | x == ""
+  |    x == ""
     || T.length y == 0
     || T.last y /= '.'   = Nothing
   | x `elem` htmls       = Just Html
@@ -215,33 +209,37 @@
 
 -- | Takes an @Accept@ header and returns the other
 -- file types handleable, in order of prescedence.
-possibleFileExts :: AcceptHeader -> [FileExt]
-possibleFileExts accept = if not (null wildcard) then wildcard else computed
+possibleFileExts :: [FileExt] -> AcceptHeader -> [FileExt]
+possibleFileExts allFileExts accept = if not (null wildcard) then wildcard else computed
   where
     computed :: [FileExt]
-    computed = concat $
-      catMaybes [ mapAccept [ ( "application/json"       :: BS.ByteString
-                              , [Json])
-                            , ( "application/javascript" :: BS.ByteString
-                              , [JavaScript,Json])
-                            ] accept
-                , mapAccept [ ( "text/html" :: BS.ByteString
-                              , [Html])
-                            ] accept
-                , mapAccept [ ( "text/plain" :: BS.ByteString
-                              , [Text, Markdown])
-                            ] accept
-                , mapAccept [ ( "text/markdown" :: BS.ByteString
-                              , [Markdown])
-                            ] accept
-                , mapAccept [ ( "text/css" :: BS.ByteString
-                              , [Css])
-                            ] accept
-                ]
+    computed = fromMaybe [] $
+      mapAccept [ ( "application/json"       :: BS.ByteString
+                  , [Json]
+                  )
+                , ( "application/javascript" :: BS.ByteString
+                  , [JavaScript,Json]
+                  )
+                , ( "text/html" :: BS.ByteString
+                  , [Html]
+                  )
+                , ( "text/css" :: BS.ByteString
+                  , [Css]
+                  )
+                , ( "text/markdown" :: BS.ByteString
+                  , [Markdown]
+                  )
+                , ( "text/plain" :: BS.ByteString
+                  , [Text, Markdown]
+                  )
+                ] accept
 
     wildcard :: [FileExt]
-    wildcard = fromMaybe [] $ mapAccept [ ("*/*" :: BS.ByteString, allFileExts)
-                                        ] accept
+    wildcard = fromMaybe [] $
+      mapAccept [ ("*/*" :: BS.ByteString
+                  , allFileExts
+                  )
+                ] accept
 
 {-# INLINEABLE possibleFileExts #-}
 
@@ -251,6 +249,6 @@
 --   >   text "foo"
 --   >   invalidEncoding myErrorHandler -- handles all except text/plain
 invalidEncoding :: Monad m => ResponseVia -> FileExtListenerT m ()
-invalidEncoding r = mapM_ (\t -> tell' $ HM.singleton t r) allFileExts
+invalidEncoding r = mapM_ (\t -> tell' $ HM.singleton t r) [Html,Css,JavaScript,Json,Text,Markdown]
 
 {-# INLINEABLE invalidEncoding #-}
diff --git a/test/Network/Wai/Middleware/ContentTypeSpec.hs b/test/Network/Wai/Middleware/ContentTypeSpec.hs
--- a/test/Network/Wai/Middleware/ContentTypeSpec.hs
+++ b/test/Network/Wai/Middleware/ContentTypeSpec.hs
@@ -11,6 +11,7 @@
 import Network.HTTP.Types
 import qualified Data.Text      as T
 import qualified Data.Text.Lazy as LT
+import qualified Data.Text.Lazy.Encoding as LT
 import qualified Lucid          as L
 import qualified Text.Lucius    as SL
 import qualified Text.Julius    as SJ
@@ -98,6 +99,12 @@
         "" { matchStatus = 200
            , matchBody = Just "*Pandoc*!"
            }
+      describe "Foo" $
+        it "should respond with 200" $
+        HW.get "/index.foo" `shouldRespondWith`
+        "" { matchStatus = 200
+           , matchBody = Just "Foo"
+           }
   describe "All Requests Respond to Both" $
     with (return app) $ do
       describe "Text" $
@@ -173,3 +180,4 @@
     case P.readMarkdown P.def "*Pandoc*!" of
       Left e -> error $ show e
       Right p -> p
+  bytestring (Other "foo") (LT.encodeUtf8 "Foo")
diff --git a/wai-middleware-content-type.cabal b/wai-middleware-content-type.cabal
--- a/wai-middleware-content-type.cabal
+++ b/wai-middleware-content-type.cabal
@@ -1,5 +1,5 @@
 Name:                   wai-middleware-content-type
-Version:                0.5.0
+Version:                0.5.0.1
 Author:                 Athan Clark <athan.clark@gmail.com>
 Maintainer:             Athan Clark <athan.clark@gmail.com>
 License:                BSD3