diff --git a/agent/customer_agent/session.py b/agent/customer_agent/session.py
index be92fb9..64973e3 100644
--- a/agent/customer_agent/session.py
+++ b/agent/customer_agent/session.py
@@ -59,8 +59,8 @@ class AnonymousSessionService:
         await self.redis.zremrangebyscore(key, 0, (now - window) * 1000)
         count = await self.redis.zcard(key)
         if count >= maximum:
-            entries = self.redis.sorted_sets.get(key, [])
-            oldest = min((score for score, _ in entries), default=now * 1000)
+            entries = await self.redis.zrange(key, 0, 0, withscores=True)
+            oldest = entries[0][1] if entries else now * 1000
             return max(1, int((oldest / 1000 + window) - now))
         await self.redis.zadd(key, {uuid.uuid4().hex: now * 1000})
         await self.redis.expire(key, window)