diff --git a/tcms/handlers.py b/tcms/handlers.py
index 2ddc6b7248..5445976e44 100644
--- a/tcms/handlers.py
+++ b/tcms/handlers.py
@@ -3,7 +3,8 @@
 from datetime import timedelta
 
 from modernrpc.handlers import JSONRPCHandler, XMLRPCHandler
-from modernrpc.handlers.base import BaseResult, SuccessResult
+from modernrpc.handlers.base import BaseResult
+from modernrpc.handlers.xmlhandler import XmlSuccessResult
 from modernrpc.handlers.jsonhandler import JsonResult, JsonSuccessResult
 
 
@@ -56,7 +57,7 @@ def escape_list(result_list):
                 __class__.escape_dict(item)
 
     def dumps_result(self, result: BaseResult) -> str:
-        if isinstance(result, SuccessResult):
+        if isinstance(result, XmlSuccessResult):
             if isinstance(result.data, timedelta):
                 result.data = result.data.total_seconds()
             elif isinstance(result.data, dict):