diff --git a/authlib/integrations/starlette_client/integration.py b/authlib/integrations/starlette_client/integration.py
index b6f68d2f..a92c8e3f 100644
--- a/authlib/integrations/starlette_client/integration.py
+++ b/authlib/integrations/starlette_client/integration.py
@@ -40,9 +40,9 @@ async def set_state_data(self, session: Optional[Dict[str, Any]], state: str, da
             await self.cache.set(key, json.dumps({'data': data}), self.expires_in)
         elif session is not None:
             # clear old state data to avoid session size growing
-            for key in list(session.keys()):
-                if key.startswith(key_prefix):
-                    session.pop(key)
+            for old_key in list(session.keys()):
+                if old_key.startswith(key_prefix):
+                    session.pop(old_key)
             now = time.time()
             session[key] = {'data': data, 'exp': now + self.expires_in}