diff --git a/server.py b/server.py
index 561d540..298f7fc 100644
--- a/server.py
+++ b/server.py
@@ -6340,8 +6340,9 @@ async def add_security_headers(request: Request, call_next):
     for header, value in security_headers.items():
         response.headers[header] = value
 
-    # Remove server identification headers
-    response.headers.pop("Server", None)
+    # Remove server identification headers (use del, not pop for MutableHeaders)
+    if "Server" in response.headers:
+        del response.headers["Server"]
 
     return response