diff --git a/Assets/Plugins/UniRx/Scripts/UnityEngineBridge/ReactiveProperty.cs b/Assets/Plugins/UniRx/Scripts/UnityEngineBridge/ReactiveProperty.cs
index d67a81e6c..c1bcac386 100644
--- a/Assets/Plugins/UniRx/Scripts/UnityEngineBridge/ReactiveProperty.cs
+++ b/Assets/Plugins/UniRx/Scripts/UnityEngineBridge/ReactiveProperty.cs
@@ -534,7 +534,7 @@ static void CancelCallback(object state)
                 }, ex => tcs.TrySetException(ex), () => tcs.TrySetCanceled());
             }
 
-            cancellationToken.Register(Callback, Tuple.Create(tcs, disposable.Disposable), false);
+            cancellationToken.Register(Callback, Tuple.Create((ICancellableTaskCompletionSource) tcs, disposable.Disposable), false);
 
             return tcs.Task;
         }