diff --git a/Control/Monad/Operational/Class.hs b/Control/Monad/Operational/Class.hs
--- a/Control/Monad/Operational/Class.hs
+++ b/Control/Monad/Operational/Class.hs
@@ -29,6 +29,7 @@
 import Control.Monad.Trans.Maybe
 import Control.Monad.Trans.List
 import Control.Monad.Trans.Error
+import Control.Monad.Trans.Except
 import Control.Monad.Trans.Identity
 import Control.Monad.Trans.Class
 import Data.Monoid
diff --git a/minioperational.cabal b/minioperational.cabal
--- a/minioperational.cabal
+++ b/minioperational.cabal
@@ -1,5 +1,5 @@
 name:                minioperational
-version:             0.4.4
+version:             0.4.5
 synopsis:            fast and simple operational monad
 description:         This package provides tiny implementation of operational monad.
 homepage:            https://github.com/fumieval/minioperational