diff --git a/common/tool_cmd.py b/common/tool_cmd.py
index c9cff2a2663f9127639e01a9e665ff16e525abf7..51239c004ef8bd1d76c5dde35fa03a8c4961e1ca 100644
--- a/common/tool_cmd.py
+++ b/common/tool_cmd.py
@@ -21,11 +21,11 @@ class ToolCmd:
         error_msg = []
         if args.perf_enable_type:
             if not args.perf_pid:
-                error_msg.append("need to specify --pid option")
+                error_msg = "need to specify --pid option"
                 return error_msg
         if not args.perf_enable_type:
             if args.perf_pid or args.perf_duration:
-                error_msg.append("need to specify --perf option")
+                error_msg = "need to specify --perf option"
                 return error_msg
         return error_msg