diff --git a/ChangeLog b/ChangeLog
index 36e1991503..756e486768 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Aug 17 20:05:29 2010  Tanaka Akira  <akr@fsij.org>
+
+	* test/ruby/test_io.rb (test_threaded_flush): test "hi" is not output
+	  twice.
+
 Tue Aug 17 15:13:28 2010  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* lib/date.rb: Re-revert the part of r28950.
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index bd4326060c..1cfcba181a 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -1619,7 +1619,9 @@ End
     }.gsub(/^\s+/, '')
     10.times.map do
       Thread.start do
-        assert_in_out_err([], src, [%q["hi!"]])
+        assert_in_out_err([], src) {|stdout, stderr|
+          assert_no_match(/hi.*hi/, stderr.join)
+        }
       end
     end.each {|th| th.join}
   end