diff --git a/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTaskExtensions.cs b/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTaskExtensions.cs
index 1e4faa1e..51555679 100644
--- a/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTaskExtensions.cs
+++ b/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTaskExtensions.cs
@@ -201,6 +201,7 @@ public static UniTask AttachExternalCancellation(this UniTask task, Cancellation
 
             if (cancellationToken.IsCancellationRequested)
             {
+                task.Forget();
                 return UniTask.FromCanceled(cancellationToken);
             }
 
@@ -224,6 +225,7 @@ public static UniTask<T> AttachExternalCancellation<T>(this UniTask<T> task, Can
 
             if (cancellationToken.IsCancellationRequested)
             {
+                task.Forget();
                 return UniTask.FromCanceled<T>(cancellationToken);
             }