diff --git a/ChangeLog b/ChangeLog
index 8966323c4e..db8d94bf29 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Nov 15 21:56:25 2011  Tanaka Akira  <akr@fsij.org>
+
+	* test/ruby/test_sleep.rb (test_sleep_5sec): 0.1sec tolerance is too
+	  small for busy environment.
+
 Tue Nov 15 20:08:55 2011  Tanaka Akira  <akr@fsij.org>
 
 	* io.c, thread.c, ext/pty/pty.c, ext/fiddle/closure.c: use
diff --git a/test/ruby/test_sleep.rb b/test/ruby/test_sleep.rb
index adc4876216..96c38fde5a 100644
--- a/test/ruby/test_sleep.rb
+++ b/test/ruby/test_sleep.rb
@@ -6,7 +6,8 @@ class TestSleep < Test::Unit::TestCase
     start = Time.now
     sleep 5
     slept = Time.now-start
-    assert_in_delta(5.0, slept, 0.1, "[ruby-core:18015]: longer than expected")
+    assert_operator(5.0, :<=, slept)
+    assert_operator(slept, :<=, 6.0, "[ruby-core:18015]: longer than expected")
   ensure
     GC.enable
   end