diff --git a/deriving-aeson.cabal b/deriving-aeson.cabal
--- a/deriving-aeson.cabal
+++ b/deriving-aeson.cabal
@@ -1,6 +1,6 @@
 cabal-version:       2.4
 name:                deriving-aeson
-version:             0.1
+version:             0.1.1
 synopsis:            Type driven generic aeson instance customisation
 description:         This package provides a newtype wrapper with
   FromJSON/ToJSON instances customisable via a phantom type parameter.
diff --git a/src/Deriving/Aeson/Stock.hs b/src/Deriving/Aeson/Stock.hs
--- a/src/Deriving/Aeson/Stock.hs
+++ b/src/Deriving/Aeson/Stock.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE DataKinds #-}
+{-# LANGUAGE PolyKinds #-}
 
 module Deriving.Aeson.Stock
   ( Prefixed
diff --git a/tests/test.hs b/tests/test.hs
--- a/tests/test.hs
+++ b/tests/test.hs
@@ -4,8 +4,10 @@
 
 import Data.Aeson
 import Deriving.Aeson
+import Deriving.Aeson.Stock
 import qualified Data.ByteString.Lazy.Char8 as BL
 
+
 data User = User
   { userId :: Int
   , userName :: String
@@ -14,7 +16,14 @@
   deriving (FromJSON, ToJSON)
   via CustomJSON '[OmitNothingFields, FieldLabelModifier (StripPrefix "user", CamelToSnake)] User
 
+data Foo = Foo { fooFoo :: Int, fooBar :: Int }
+  deriving Generic
+  deriving (FromJSON, ToJSON)
+  via Prefixed "foo" Foo
+
 testData :: [User]
 testData = [User 42 "Alice" Nothing, User 43 "Bob" (Just "xyz")]
 
-main = BL.putStrLn $ encode testData
+main = do
+  BL.putStrLn $ encode testData
+  BL.putStrLn $ encode $ Foo 0 1