diff --git a/ChangeLog b/ChangeLog
index cb03e2df6c..6cf7a0f0eb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+Mon Dec 21 18:33:00 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* gc.c (internal_object_p): should not expose singleton classes
+	  without a metaclass.
+	  [Bug #11740]
+
+	* class.c (rb_singleton_class_has_metaclass_p): added.
+
+	* test/ruby/test_class.rb: add a test.
+
 Mon Dec 21 12:15:32 2015  Kimura Wataru  <kimuraw@i.nifty.jp>
 
 	* test/ruby/test_io.rb: handled rlimit value same as r52277
diff --git a/class.c b/class.c
index f95890bbc4..fdebee8933 100644
--- a/class.c
+++ b/class.c
@@ -442,6 +442,12 @@ rb_singleton_class_attached(VALUE klass, VALUE obj)
  */
 #define META_CLASS_OF_CLASS_CLASS_P(k)  (METACLASS_OF(k) == (k))
 
+int
+rb_singleton_class_has_metaclass_p(VALUE sklass)
+{
+    return rb_attr_get(METACLASS_OF(sklass), id_attached) == sklass;
+}
+
 /*!
  * whether k has a metaclass
  * @retval 1 if \a k has a metaclass
@@ -449,7 +455,13 @@ rb_singleton_class_attached(VALUE klass, VALUE obj)
  */
 #define HAVE_METACLASS_P(k) \
     (FL_TEST(METACLASS_OF(k), FL_SINGLETON) && \
-     rb_ivar_get(METACLASS_OF(k), id_attached) == (k))
+     rb_singleton_class_has_metaclass_p(k))
+
+int
+rb_class_has_metaclass_p(VALUE klass)
+{
+    return HAVE_METACLASS_P(klass);
+}
 
 /*!
  * ensures \a klass belongs to its own eigenclass.
diff --git a/gc.c b/gc.c
index 12be1eac11..a57addf1c4 100644
--- a/gc.c
+++ b/gc.c
@@ -2400,6 +2400,13 @@ internal_object_p(VALUE obj)
 	  case T_NODE:
 	  case T_ZOMBIE:
 	    break;
+	  case T_CLASS:
+	    {
+		if (FL_TEST(obj, FL_SINGLETON)) {
+		    int rb_singleton_class_has_metaclass_p(VALUE sklass);
+		    return rb_singleton_class_has_metaclass_p(obj) == 0;
+		}
+	    }
 	  default:
 	    if (!p->as.basic.klass) break;
 	    return 0;
diff --git a/test/ruby/test_class.rb b/test/ruby/test_class.rb
index e60db37c15..81c11e6f88 100644
--- a/test/ruby/test_class.rb
+++ b/test/ruby/test_class.rb
@@ -556,4 +556,24 @@ class TestClass < Test::Unit::TestCase
       }
     end;
   end
+
+  def test_should_not_expose_singleton_class_without_metaclass
+    assert_normal_exit %q{
+      klass = Class.new(Array)
+      # The metaclass of +klass+ should handle #bla since it should inherit methods from meta:meta:Array
+      def (Array.singleton_class).bla; :bla; end
+      hidden = ObjectSpace.each_object(Class).find { |c| klass.is_a? c and c.inspect.include? klass.inspect }
+      raise unless hidden.nil?
+    }, '[Bug #11740]'
+
+    assert_normal_exit %q{
+      klass = Class.new(Array)
+      klass.singleton_class
+      # The metaclass of +klass+ should handle #bla since it should inherit methods from meta:meta:Array
+      def (Array.singleton_class).bla; :bla; end
+      hidden = ObjectSpace.each_object(Class).find { |c| klass.is_a? c and c.inspect.include? klass.inspect }
+      raise if hidden.nil?
+    }, '[Bug #11740]'
+
+  end
 end