diff --git a/api/core/workflow/graph_engine/worker_management/worker_pool.py b/api/core/workflow/graph_engine/worker_management/worker_pool.py
index 25671ce6ba..00328fbda1 100644
--- a/api/core/workflow/graph_engine/worker_management/worker_pool.py
+++ b/api/core/workflow/graph_engine/worker_management/worker_pool.py
@@ -217,7 +217,7 @@ class WorkerPool:
             return False
 
         # Find and remove idle workers that have been idle long enough
-        workers_to_remove = []
+        workers_to_remove: list[tuple[Worker, int]] = []
 
         for worker in self._workers:
             # Check if worker is idle and has exceeded idle time threshold