diff --git a/hw-prim.cabal b/hw-prim.cabal
--- a/hw-prim.cabal
+++ b/hw-prim.cabal
@@ -1,5 +1,5 @@
 name:                   hw-prim
-version:                0.0.3.0
+version:                0.0.3.1
 synopsis:               Primitive functions and data types
 description:            Please see README.md
 homepage:               http://github.com/haskell-works/hw-prim#readme
diff --git a/src/HaskellWorks/Data/Decode.hs b/src/HaskellWorks/Data/Decode.hs
--- a/src/HaskellWorks/Data/Decode.hs
+++ b/src/HaskellWorks/Data/Decode.hs
@@ -5,7 +5,7 @@
   , DecodeError(..)
   ) where
 
-data DecodeError = DecodeError String
+data DecodeError = DecodeError String deriving (Eq, Show)
 
 class Decode s t where
   decode :: s -> Either DecodeError t