diff -r 55bea11d892e Lib/test/test_descr.py
--- a/Lib/test/test_descr.py	Thu Mar 10 08:44:08 2011 -0500
+++ b/Lib/test/test_descr.py	Thu Mar 10 19:46:49 2011 +0100
@@ -4235,6 +4235,19 @@
         with self.assertRaises(AttributeError):
             del X.__abstractmethods__
 
+    def test_issue11455(self):
+        # issue11455: issue a warning when the
+        # __dict__ of a class contains non-string keys
+        with self.assertWarnsRegex(RuntimeWarning, 'MyClass'):
+            MyClass = type('MyClass', (), {1: 2})
+
+        class meta(type):
+            def __new__(mcls, name, bases, ns):
+                ns[1] = 2
+                return super().__new__(mcls, name, bases, ns)
+        with self.assertWarnsRegex(RuntimeWarning, 'MyClass'):
+            MyClass = meta('MyClass', (), {})
+
 
 class DictProxyTests(unittest.TestCase):
     def setUp(self):
diff -r 55bea11d892e Objects/typeobject.c
--- a/Objects/typeobject.c	Thu Mar 10 08:44:08 2011 -0500
+++ b/Objects/typeobject.c	Thu Mar 10 19:46:49 2011 +0100
@@ -2316,6 +2316,19 @@
     /* Put the proper slots in place */
     fixup_slot_dispatchers(type);
 
+    if (!_PyDict_HasOnlyStringKeys(type->tp_dict)) {
+        PyObject *name_of_class = type_name(type, NULL);
+        if (name_of_class == NULL) {
+            Py_DECREF(type);
+            return NULL;
+        }
+
+        if (PyErr_WarnFormat(NULL, 1, "non-string key in the __dict__ of class %U", name_of_class) == -1) {
+            Py_DECREF(type);
+            return NULL;
+        }
+    }
+
     return (PyObject *)type;
 }