diff --git a/domain/tasks/subtasks.py b/domain/tasks/subtasks.py
index bd49a6ec6..95f9ec5bc 100644
--- a/domain/tasks/subtasks.py
+++ b/domain/tasks/subtasks.py
@@ -35,11 +35,14 @@ class SubTask:
         )
 
     def start(self, cloud_logs_url: Optional[str] = None) -> None:
-        if self.status not in (SubTaskStatus.WAITING, SubTaskStatus.IN_PROGRESS):
+        # FAILED may restart: a failed batch is re-run by re-sending its own
+        # inputs, and its completion un-fails the parent Task (ADR-0055).
+        if self.status is SubTaskStatus.COMPLETE:
             raise ValueError(f"cannot start subtask in status {self.status}")
         if self.job_started is None:
             self.job_started = datetime.now(timezone.utc)
         self.status = SubTaskStatus.IN_PROGRESS
+        self.job_completed = None
         if cloud_logs_url is not None:
             self.cloud_logs_url = cloud_logs_url