diff --git a/moffy-samples-events.cabal b/moffy-samples-events.cabal
--- a/moffy-samples-events.cabal
+++ b/moffy-samples-events.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           moffy-samples-events
-version:        0.2.2.2
+version:        0.2.2.3
 synopsis:       Events for sample codes of moffy
 description:    Please see the README on GitHub at <https://github.com/YoshikuniJujo/moffy-samples-events#readme>
 category:       Control
diff --git a/src/Control/Moffy/Samples/Handle/Area.hs b/src/Control/Moffy/Samples/Handle/Area.hs
--- a/src/Control/Moffy/Samples/Handle/Area.hs
+++ b/src/Control/Moffy/Samples/Handle/Area.hs
@@ -22,4 +22,4 @@
 
 handleGetArea :: TVar (M.Map Int (Point, Point)) -> Handle' IO (Singleton GetArea)
 handleGetArea vm (Oom.Singleton (GetAreaReq i)) = do
-	Just . App.Singleton . uncurry (OccGetArea i) <$> atomically ((M.! i) <$> readTVar vm)
+	(App.Singleton . uncurry (OccGetArea i) <$>) <$> atomically ((M.lookup i) <$> readTVar vm)