diff --git a/Codec/Encryption/AES.hs b/Codec/Encryption/AES.hs
--- a/Codec/Encryption/AES.hs
+++ b/Codec/Encryption/AES.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE TypeSynonymInstances #-}
+{-# LANGUAGE TypeSynonymInstances, FlexibleInstances #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Codec.Encryption.AES
diff --git a/Crypto.cabal b/Crypto.cabal
--- a/Crypto.cabal
+++ b/Crypto.cabal
@@ -1,5 +1,5 @@
 Name:            Crypto
-Version:         4.2.3
+Version:         4.2.4
 License:         OtherLicense
 License-File:    ReadMe.tex
 Author:          Dominic Steinitz
diff --git a/QuickTest.hs b/QuickTest.hs
--- a/QuickTest.hs
+++ b/QuickTest.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE TypeSynonymInstances #-}
+{-# LANGUAGE TypeSynonymInstances, FlexibleInstances #-}
 
 module Main where