diff --git a/ChangeLog b/ChangeLog
index 7a4154507a..ea8f937ae1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Sun Jun 19 10:05:16 2011  Shota Fukumori  <sorah@tubusu.net>
+
+	* lib/test/unit/parallel.rb: Override Test::Unit::TestCase#on_parallel_worker?
+	  only when $0 == __FILE__.
+
+	* lib/test/unit/parallel.rb: Run Test::Unit::Worker.run only when
+	  $0 == __FILE__.
+
 Sat Jun 18 23:59:24 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* io.c (fill_cbuf): finish reading at EOF, and the readconv has
diff --git a/lib/test/unit/parallel.rb b/lib/test/unit/parallel.rb
index ab9e864509..7a7c73d4f2 100644
--- a/lib/test/unit/parallel.rb
+++ b/lib/test/unit/parallel.rb
@@ -2,12 +2,6 @@ require 'test/unit'
 
 module Test
   module Unit
-    class TestCase < MiniTest::Unit::TestCase
-      def on_parallel_worker?
-        true
-      end
-    end
-
     class Worker < Runner
       class << self
         undef autorun
@@ -148,4 +142,16 @@ module Test
   end
 end
 
-Test::Unit::Worker.new.run(ARGV)
+if $0 == __FILE__
+  module Test
+    module Unit
+      class TestCase < MiniTest::Unit::TestCase
+        def on_parallel_worker?
+          true
+        end
+      end
+    end
+  end
+
+  Test::Unit::Worker.new.run(ARGV)
+end