diff --git a/Web/Authenticate/OpenId.hs b/Web/Authenticate/OpenId.hs
--- a/Web/Authenticate/OpenId.hs
+++ b/Web/Authenticate/OpenId.hs
@@ -26,19 +26,12 @@
 import Control.Monad.Trans
 import qualified Safe.Failure as A
 import Data.Generics
-import Control.Monad.Failure
+import Control.Failure
 import Control.Exception
 
 -- | An openid identifier (ie, a URL).
 newtype Identifier = Identifier { identifier :: String }
     deriving (Eq, Show)
-
-data Error v = Error String | Ok v
-instance Monad Error where
-    return = Ok
-    Error s >>= _ = Error s
-    Ok v >>= f = f v
-    fail s = Error s
 
 -- | Returns a URL to forward the user to in order to login.
 getForwardUrl :: (MonadIO m, MonadFailure WgetException m)
diff --git a/Web/Authenticate/Rpxnow.hs b/Web/Authenticate/Rpxnow.hs
--- a/Web/Authenticate/Rpxnow.hs
+++ b/Web/Authenticate/Rpxnow.hs
@@ -21,7 +21,7 @@
 import Network.HTTP.Wget
 import Data.Maybe (isJust, fromJust)
 import Control.Monad.Trans
-import Control.Monad.Failure
+import Control.Failure
 
 -- | Information received from Rpxnow after a valid login.
 data Identifier = Identifier
diff --git a/authenticate.cabal b/authenticate.cabal
--- a/authenticate.cabal
+++ b/authenticate.cabal
@@ -1,5 +1,5 @@
 name:            authenticate
-version:         0.2.1
+version:         0.4.0
 license:         BSD3
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>
@@ -15,12 +15,12 @@
 
 library
     build-depends:   base >= 4 && < 5,
-                     json,
-                     http-wget >= 0.2.1,
-                     tagsoup,
-                     control-monad-failure,
-                     safe-failure,
-                     transformers >= 0.1.4.0,
+                     json >= 0.4.3 && < 0.5,
+                     http-wget >= 0.4.0 && < 0.5,
+                     tagsoup >= 0.6 && < 0.7,
+                     failure >= 0.0.0 && < 0.1,
+                     safe-failure >= 0.4 && < 0.5,
+                     transformers >= 0.1.4.0 && < 0.2,
                      syb
     exposed-modules: Web.Authenticate.Rpxnow,
                      Web.Authenticate.OpenId