diff --git a/python/sglang/srt/managers/session_controller.py b/python/sglang/srt/managers/session_controller.py
index 7e545ff87..1148f9f82 100644
--- a/python/sglang/srt/managers/session_controller.py
+++ b/python/sglang/srt/managers/session_controller.py
@@ -19,7 +19,12 @@ from sglang.srt.managers.schedule_batch import FINISH_ABORT, Req
 
 
 class SessionReqNode:
-    def __init__(self, req: Req, parent=None, childs=None):
+    def __init__(
+        self,
+        req: Req,
+        parent: Optional["SessionReqNode"] = None,
+        childs=None,
+    ):
         self.req = req
         self.parent = parent
         if parent is not None: