diff --git a/test/readline/test_readline.rb b/test/readline/test_readline.rb
index 4baf43943f..44eb0a33c2 100644
--- a/test/readline/test_readline.rb
+++ b/test/readline/test_readline.rb
@@ -519,6 +519,7 @@ module BasetestReadline
 
     EnvUtil.invoke_ruby(["-I#{__dir__}", script.path], "", true, :merge_to_stdout) do |_in, _out, _, pid|
       Timeout.timeout(TIMEOUT) do
+        log << "** START **"
         while c = _out.read(1)
           log << c if c
           break if log.include?('input>')