diff --git a/Web/Authenticate/OAuth.hs b/Web/Authenticate/OAuth.hs
--- a/Web/Authenticate/OAuth.hs
+++ b/Web/Authenticate/OAuth.hs
@@ -35,7 +35,7 @@
 import Data.Time
 import Numeric
 import Codec.Crypto.RSA (rsassa_pkcs1_v1_5_sign, ha_SHA1)
-import Crypto.Types.PubKey.RSA (PrivateKey(..))
+import Crypto.Types.PubKey.RSA (PrivateKey(..), PublicKey(..))
 import Network.HTTP.Types (Header)
 import Blaze.ByteString.Builder (toByteString)
 import Control.Monad.IO.Class (MonadIO)
@@ -110,6 +110,8 @@
                 | RSASHA1 PrivateKey
                   deriving (Show, Eq, Ord, Read, Data, Typeable)
 deriving instance Ord PrivateKey
+deriving instance Ord PublicKey
+
 -- | Data type for redential.
 data Credential = Credential { unCredential :: [(BS.ByteString, BS.ByteString)] }
                   deriving (Show, Eq, Ord, Read, Data, Typeable)
diff --git a/authenticate-oauth.cabal b/authenticate-oauth.cabal
--- a/authenticate-oauth.cabal
+++ b/authenticate-oauth.cabal
@@ -1,6 +1,6 @@
 
 name:            authenticate-oauth
-version:         1.4.0.3
+version:         1.4.0.4
 license:         BSD3
 license-file:    LICENSE
 author:          Hiromi Ishii