diff -r 218e28a935ab Lib/test/test_py3kwarn.py
--- a/Lib/test/test_py3kwarn.py	Sat Apr 12 09:31:28 2014 -0700
+++ b/Lib/test/test_py3kwarn.py	Mon Apr 14 23:00:38 2014 -0400
@@ -78,7 +78,7 @@
                 safe_exec("def {0}(): pass".format(keyword))
                 self.assertWarning(None, w, expected)
                 w.reset()
-                safe_exec("class {0}: pass".format(keyword))
+                safe_exec("class {0}(object): pass".format(keyword))
                 self.assertWarning(None, w, expected)
                 w.reset()
                 safe_exec("def f({0}=43): pass".format(keyword))
@@ -307,6 +307,14 @@
             w.reset()
             self.assertWarning(sequenceIncludes(range(3), 2), w, seq_warn)
 
+    def test_oldstyle_class(self):
+        expected = ('Old-style classes are removed in 3.x. All classes should '
+            'subclass object.')
+        def check(s):
+            with check_py3k_warnings((expected, DeprecationWarning)):
+                exec s in {}
+        check("class X: pass")
+
 
 class TestStdlibRemovals(unittest.TestCase):
 
diff -r 218e28a935ab Python/ceval.c
--- a/Python/ceval.c	Sat Apr 12 09:31:28 2014 -0700
+++ b/Python/ceval.c	Mon Apr 14 23:00:38 2014 -0400
@@ -4625,6 +4625,10 @@
         if (g != NULL && PyDict_Check(g))
             metaclass = PyDict_GetItemString(g, "__metaclass__");
         if (metaclass == NULL)
+            if (PyErr_WarnPy3k("Old-style classes are removed in 3.x. All "
+                               "classes should subclass object.", 0) < 0) {
+                return NULL;
+            }
             metaclass = (PyObject *) &PyClass_Type;
         Py_INCREF(metaclass);
     }