diff --git a/src/Network/Wai/Middleware/ContentType/Lucid.hs b/src/Network/Wai/Middleware/ContentType/Lucid.hs
--- a/src/Network/Wai/Middleware/ContentType/Lucid.hs
+++ b/src/Network/Wai/Middleware/ContentType/Lucid.hs
@@ -9,7 +9,6 @@
 
 import qualified Lucid.Base                              as L
 import           Control.Monad.Trans
-import           Control.Monad.IO.Class                  (MonadIO)
 
 
 
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
@@ -69,3 +69,12 @@
 
 execFileExtListenerT :: Monad m => FileExtListenerT r m a -> m (FileExts r)
 execFileExtListenerT xs = execStateT (runFileExtListenerT xs) mempty
+
+mapFileExts :: Monad m =>
+               (a -> b)
+            -> FileExtListenerT a m () -> FileExtListenerT b m ()
+mapFileExts f fl = do
+  femap <- lift $ execFileExtListenerT fl
+  tell $ f <$> femap
+
+
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:                0.0.1
+Version:                0.0.2
 Author:                 Athan Clark <athan.clark@gmail.com>
 Maintainer:             Athan Clark <athan.clark@gmail.com>
 License:                BSD3