diff --git a/test/ruby/test_variable.rb b/test/ruby/test_variable.rb
index aa301f2bc7..f14b4019df 100644
--- a/test/ruby/test_variable.rb
+++ b/test/ruby/test_variable.rb
@@ -35,6 +35,34 @@ class TestVariable < Test::Unit::TestCase
     end
   end
 
+  def test_singleton_class_included_class_variable
+    c = Class.new
+    c.extend(Olympians)
+    assert_empty(c.singleton_class.class_variables)
+    assert_raise(NameError){ c.singleton_class.class_variable_get(:@@rule) }
+    c.class_variable_set(:@@foo, 1)
+    assert_equal([:@@foo], c.singleton_class.class_variables)
+    assert_equal(1, c.singleton_class.class_variable_get(:@@foo))
+    
+    c = Class.new
+    c.extend(Olympians)
+    sc = Class.new(c)
+    assert_empty(sc.singleton_class.class_variables)
+    assert_raise(NameError){ sc.singleton_class.class_variable_get(:@@rule) }
+    c.class_variable_set(:@@foo, 1)
+    assert_equal([:@@foo], sc.singleton_class.class_variables)
+    assert_equal(1, sc.singleton_class.class_variable_get(:@@foo))
+
+    c = Class.new
+    o = c.new
+    o.extend(Olympians)
+    assert_equal([:@@rule], o.singleton_class.class_variables)
+    assert_equal("Zeus", o.singleton_class.class_variable_get(:@@rule))
+    c.class_variable_set(:@@foo, 1)
+    assert_equal([:@@foo, :@@rule], o.singleton_class.class_variables.sort)
+    assert_equal(1, o.singleton_class.class_variable_get(:@@foo))
+  end
+
   def test_variable
     assert_instance_of(Integer, $$)
 
diff --git a/variable.c b/variable.c
index f3d73fac63..1627467bd9 100644
--- a/variable.c
+++ b/variable.c
@@ -3209,6 +3209,12 @@ static void*
 mod_cvar_of(VALUE mod, void *data)
 {
     VALUE tmp = mod;
+    if (FL_TEST(mod, FL_SINGLETON)) {
+        if (rb_namespace_p(rb_ivar_get(mod, id__attached__))) {
+            data = mod_cvar_at(tmp, data);
+            tmp = cvar_front_klass(tmp);
+        }
+    }
     for (;;) {
 	data = mod_cvar_at(tmp, data);
 	tmp = RCLASS_SUPER(tmp);