diff --git a/python/ray/data/_internal/execution/operators/map_operator.py b/python/ray/data/_internal/execution/operators/map_operator.py
index c665d035a1c5..fe33c99f558c 100644
--- a/python/ray/data/_internal/execution/operators/map_operator.py
+++ b/python/ray/data/_internal/execution/operators/map_operator.py
@@ -330,7 +330,7 @@ def _task_done_callback(task_index: int, exception: Optional[Exception]):
                     * self._metrics.num_outputs_of_finished_tasks
                     / self._metrics.num_tasks_finished
                 )
-                self._estimated_num_output_rows = round(
+                self._estimated_output_num_rows = round(
                     estimated_num_tasks
                     * self._metrics.rows_task_outputs_generated
                     / self._metrics.num_tasks_finished