diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 ## Changelog
 
+#### 0.3.3.5 (2014-04-29)
+
+* Update to `fay 0.20`
+
 #### 0.3.3.4 (2014-01-19)
 
 * Allow aeson 0.7.*
diff --git a/snaplet-fay.cabal b/snaplet-fay.cabal
--- a/snaplet-fay.cabal
+++ b/snaplet-fay.cabal
@@ -1,5 +1,5 @@
 name:                snaplet-fay
-version:             0.3.3.4
+version:             0.3.3.5
 synopsis:            Fay integration for Snap with request- and pre-compilation.
 description:         Fay integration for Snap with request based compilation during development and precompilation in production.
                      For more information, please see <https://github.com/bergmark/snaplet-fay>.
@@ -56,7 +56,7 @@
     , configurator == 0.2.*
     , data-default == 0.5.*
     , directory    >= 1.1 && < 1.3
-    , fay          >= 0.18.0.2 && < 0.20
+    , fay          == 0.20.*
     , filepath     == 1.3.*
     , mtl          == 2.1.*
     , snap         >= 0.11.1 && < 0.14
diff --git a/src/Snap/Snaplet/Fay.hs b/src/Snap/Snaplet/Fay.hs
--- a/src/Snap/Snaplet/Fay.hs
+++ b/src/Snap/Snaplet/Fay.hs
@@ -112,7 +112,7 @@
 -- | JSON response.
 -- | If you only want to send JSON and handle input manually, use toFayax.
 -- | If you want to receive JSON and handle the response manually, use fromFayax
-fayax :: (Data f1, Read f1, Show f2) => (f1 -> Handler h1 h2 f2) -> Handler h1 h2 ()
+fayax :: (Data f1, Read f1, Data f2) => (f1 -> Handler h1 h2 f2) -> Handler h1 h2 ()
 fayax g = do
   res <- decode
   case res of
@@ -120,7 +120,7 @@
     Right res -> toFayax . g $ res
 
 -- | fayax only sending JSON.
-toFayax :: Show f2 => Handler h1 h2 f2 -> Handler h1 h2 ()
+toFayax :: Data f2 => Handler h1 h2 f2 -> Handler h1 h2 ()
 toFayax g = do
   modifyResponse . setContentType $ "text/json;charset=utf-8"
   writeLBS . A.encode . showToFay =<< g
diff --git a/src/Snap/Snaplet/Fay/Internal.hs b/src/Snap/Snaplet/Fay/Internal.hs
--- a/src/Snap/Snaplet/Fay/Internal.hs
+++ b/src/Snap/Snaplet/Fay/Internal.hs
@@ -5,15 +5,13 @@
 
 import           Control.Applicative
 import           Control.Monad
-import qualified Data.Aeson as A
+import qualified Data.Aeson                 as A
 import qualified Data.ByteString.Lazy.Char8 as C
 import           Data.Default
-import qualified Fay as F
-import qualified Fay.Compiler.Config as F
+import qualified Fay                        as F
 import           System.Directory
 import           System.FilePath
 
-
 -- | Configuration
 data Fay = Fay {
     snapletFilePath :: FilePath
@@ -60,7 +58,7 @@
                                             , F.configFilePath = Just f'
                                             }
       case res of
-        Right (out, _sourceMap) -> do
+        Right out -> do
           verbosePut config $ "Compiled " ++ hsRelativePath f
           writeFile (jsPath config f) out
           return $ Success out