1 files changed, 14 insertions, 1 deletions
diff --git a/class.c b/class.c
index f95890bbc4..a72f4dcebd 100644
--- a/class.c
+++ b/class.c
@@ -442,6 +442,19 @@ rb_singleton_class_attached(VALUE klass, VALUE obj)
  */
 #define META_CLASS_OF_CLASS_CLASS_P(k)  (METACLASS_OF(k) == (k))
 
+static int
+rb_singleton_class_has_metaclass_p(VALUE sklass)
+{
+    return rb_attr_get(METACLASS_OF(sklass), id_attached) == sklass;
+}
+
+int
+rb_singleton_class_internal_p(VALUE sklass)
+{
+    return (RB_TYPE_P(rb_attr_get(sklass, id_attached), T_CLASS) &&
+	    !rb_singleton_class_has_metaclass_p(sklass));
+}
+
 /*!
  * whether k has a metaclass
  * @retval 1 if \a k has a metaclass
@@ -449,7 +462,7 @@ 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))
 
 /*!
  * ensures \a klass belongs to its own eigenclass.