diff --git a/python/sglang/bench_serving.py b/python/sglang/bench_serving.py
index db22f42c4..036d1e864 100644
--- a/python/sglang/bench_serving.py
+++ b/python/sglang/bench_serving.py
@@ -1006,7 +1006,7 @@ async def benchmark(
 
     # Flush cache
     if "sglang" in backend:
-        requests.post(base_url + "/flush_cache")
+        requests.post(base_url + "/flush_cache", headers=get_auth_headers())
 
     time.sleep(1.0)