diff --git a/ChangeLog b/ChangeLog
index b88dc87aee..ed7c82149d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Wed Aug  1 00:33:19 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* class.c (include_class_new): fix duplication of prepended module.
+	  since m_tbl of prepended module is always zero, copy from its
+	  copy iclass of original.
+
 Tue Jul 31 18:22:34 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* variable.c (classname): tell if found name is permanent.  search
diff --git a/class.c b/class.c
index d81c093c9c..1253ce80b7 100644
--- a/class.c
+++ b/class.c
@@ -636,7 +636,7 @@ include_class_new(VALUE module, VALUE super)
     }
     RCLASS_IV_TBL(klass) = RCLASS_IV_TBL(module);
     RCLASS_CONST_TBL(klass) = RCLASS_CONST_TBL(module);
-    RCLASS_M_TBL(klass) = RCLASS_M_TBL(module);
+    RCLASS_M_TBL(klass) = RCLASS_M_TBL(RCLASS_ORIGIN(module));
     RCLASS_SUPER(klass) = super;
     if (RB_TYPE_P(module, T_ICLASS)) {
 	RBASIC(klass)->klass = RBASIC(module)->klass;
diff --git a/test/ruby/test_module.rb b/test/ruby/test_module.rb
index 43e80a5955..4e5f8856a6 100644
--- a/test/ruby/test_module.rb
+++ b/test/ruby/test_module.rb
@@ -1356,6 +1356,15 @@ class TestModule < Test::Unit::TestCase
     assert_equal([:m0, :m1, :m2, :c1], c1.new.x)
     assert_equal([c2, m0, m1, m2, c0], c2.ancestors[0, 5], bug6662)
     assert_equal([:c2, :m0, :m1, :m2, :c0], c2.new.x)
+
+    m3 = labeled_module("m3") {include m1; prepend m1}
+    assert_equal([m3, m0, m1], m3.ancestors)
+    m3 = labeled_module("m3") {prepend m1; include m1}
+    assert_equal([m0, m1, m3], m3.ancestors)
+    m3 = labeled_module("m3") {prepend m1; prepend m1}
+    assert_equal([m0, m1, m3], m3.ancestors)
+    m3 = labeled_module("m3") {include m1; include m1}
+    assert_equal([m3, m0, m1], m3.ancestors)
   end
 
   def labeled_module(name, &block)