diff --git a/object.c b/object.c
index 6c0aa040b9..15c6f960db 100644
--- a/object.c
+++ b/object.c
@@ -497,6 +497,12 @@ rb_obj_itself(VALUE obj)
     return obj;
 }
 
+static VALUE
+rb_obj_size(VALUE self, VALUE args, VALUE obj)
+{
+    return LONG2FIX(1);
+}
+
 /*
  *  call-seq:
  *     obj.yield_self {|_obj|...} -> an_object
@@ -510,7 +516,7 @@ rb_obj_itself(VALUE obj)
 static VALUE
 rb_obj_yield_self(VALUE obj)
 {
-    RETURN_ENUMERATOR(obj, 0, 0);
+    RETURN_SIZED_ENUMERATOR(obj, 0, 0, rb_obj_size);
     return rb_yield_values2(1, &obj);
 }
 
diff --git a/test/ruby/test_object.rb b/test/ruby/test_object.rb
index 6a1a82546a..1e952533a6 100644
--- a/test/ruby/test_object.rb
+++ b/test/ruby/test_object.rb
@@ -23,7 +23,9 @@ class TestObject < Test::Unit::TestCase
     object = Object.new
     assert_same(self, object.yield_self {self}, feature)
     assert_same(object, object.yield_self {|x| break x}, feature)
-    assert_instance_of(Enumerator, object.yield_self)
+    enum = object.yield_self
+    assert_instance_of(Enumerator, enum)
+    assert_equal(1, enum.size)
   end
 
   def test_dup