diff --git a/backend/oasst_backend/prompt_repository.py b/backend/oasst_backend/prompt_repository.py
index b805a4d7..dacd5f9b 100644
--- a/backend/oasst_backend/prompt_repository.py
+++ b/backend/oasst_backend/prompt_repository.py
@@ -160,7 +160,12 @@ class PromptRepository:
         return message
 
     def _validate_task(
-        self, task: Task, *, task_id: Optional[UUID] = None, frontend_message_id: Optional[str] = None
+        self,
+        task: Task,
+        *,
+        task_id: Optional[UUID] = None,
+        frontend_message_id: Optional[str] = None,
+        check_ack: bool = True,
     ) -> Task:
         if task is None:
             if task_id:
@@ -171,7 +176,7 @@ class PromptRepository:
 
         if task.expired:
             raise OasstError("Task already expired.", OasstErrorCode.TASK_EXPIRED)
-        if not task.ack:
+        if check_ack and not task.ack:
             raise OasstError("Task is not acknowledged.", OasstErrorCode.TASK_NOT_ACK)
         if task.done:
             raise OasstError("Task already done.", OasstErrorCode.TASK_ALREADY_DONE)
@@ -1021,7 +1026,7 @@ WHERE message.id = cc.id;
         self.ensure_user_is_enabled()
 
         task = self.task_repository.fetch_task_by_id(task_id)
-        self._validate_task(task)
+        self._validate_task(task, check_ack=False)
 
         if not task.collective:
             task.skipped = True