diff --git a/Happstack/Lite.hs b/Happstack/Lite.hs
--- a/Happstack/Lite.hs
+++ b/Happstack/Lite.hs
@@ -56,6 +56,7 @@
      ) where
 
 import Control.Monad (MonadPlus(..), msum)
+import Control.Monad.Trans (liftIO)
 import qualified Data.ByteString as B
 import Data.ByteString.Lazy.Char8 (ByteString)
 import Data.Int (Int64)
@@ -442,7 +443,7 @@
 serveFile :: (FilePath -> IO String)   -- ^ function for determining content-type of file. Typically 'asContentType'
           -> FilePath                 -- ^ path to the file to serve
           -> ServerPart Response
-serveFile = S.serveFile
+serveFile asContentType fp = S.serveFile (liftIO . asContentType) fp
 
 
 -- | returns a specific content type, completely ignoring the 'FilePath' argument.
diff --git a/happstack-lite.cabal b/happstack-lite.cabal
--- a/happstack-lite.cabal
+++ b/happstack-lite.cabal
@@ -1,5 +1,5 @@
 Name:                happstack-lite
-Version:             7.1.0
+Version:             7.1.1
 Synopsis:            Happstack minus the useless stuff
 Description:         This packages provides a subset of Happstack that is easier to learn but still very useful. It as 100% compatible with the full version of Happstack.
 Homepage:            http://www.happstack.com/
@@ -19,4 +19,5 @@
   Build-depends: base             < 5,
                  bytestring       == 0.9.*,
                  happstack-server == 7.0.*,
+                 mtl              >= 2 && < 2.2,
                  text             == 0.11.*