diff -r a1235865dd54 Lib/test/test_abc.py
--- a/Lib/test/test_abc.py	Sat Apr 09 13:00:17 2011 -0700
+++ b/Lib/test/test_abc.py	Sat Apr 09 22:27:18 2011 -0400
@@ -263,6 +263,37 @@
         C()
         self.assertEqual(B.counter, 1)
 
+    def test_builtin_classes(self):
+        class DirectDict(dict, metaclass=abc.ABCMeta):
+            @abc.abstractmethod
+            def foo():
+                pass
+        class DirectTuple(tuple, metaclass=abc.ABCMeta):
+            @abc.abstractmethod
+            def foo():
+                pass
+
+        class Base(metaclass=abc.ABCMeta):
+            @abc.abstractmethod
+            def foo():
+                pass
+        class Dict(dict, Base):
+           pass
+        class Tuple(tuple, Base):
+           pass
+        class List(list, Base):
+           pass
+        class Str(str, Base):
+           pass
+
+        self.assertRaises(TypeError, DirectDict)
+        self.assertRaises(TypeError, DirectTuple)
+        self.assertRaises(TypeError, Base)
+        self.assertRaises(TypeError, Dict)
+        self.assertRaises(TypeError, Tuple)
+        self.assertRaises(TypeError, List)
+        self.assertRaises(TypeError, Str)
+
 
 def test_main():
     support.run_unittest(TestABC)
diff -r a1235865dd54 Objects/typeobject.c
--- a/Objects/typeobject.c	Sat Apr 09 13:00:17 2011 -0700
+++ b/Objects/typeobject.c	Sat Apr 09 22:27:18 2011 -0400
@@ -700,9 +700,56 @@
 PyType_GenericAlloc(PyTypeObject *type, Py_ssize_t nitems)
 {
     PyObject *obj;
-    const size_t size = _PyObject_VAR_SIZE(type, nitems+1);
+    size_t size;
     /* note that we need to add one, for the sentinel */
 
+    if (type->tp_flags & Py_TPFLAGS_IS_ABSTRACT) {
+        static PyObject *comma = NULL;
+        PyObject *abstract_methods = NULL;
+        PyObject *builtins;
+        PyObject *sorted;
+        PyObject *sorted_methods = NULL;
+        PyObject *joined = NULL;
+
+        /* Compute ", ".join(sorted(type.__abstractmethods__))
+           into joined. */
+        abstract_methods = type_abstractmethods(type, NULL);
+        if (abstract_methods == NULL)
+            goto error;
+        builtins = PyEval_GetBuiltins();
+        if (builtins == NULL)
+            goto error;
+        sorted = PyDict_GetItemString(builtins, "sorted");
+        if (sorted == NULL)
+            goto error;
+        sorted_methods = PyObject_CallFunctionObjArgs(sorted,
+                                                      abstract_methods,
+                                                      NULL);
+        if (sorted_methods == NULL)
+            goto error;
+        if (comma == NULL) {
+            comma = PyUnicode_InternFromString(", ");
+            if (comma == NULL)
+                goto error;
+        }
+        joined = PyObject_CallMethod(comma, "join",
+                                     "O",  sorted_methods);
+        if (joined == NULL)
+            goto error;
+
+        PyErr_Format(PyExc_TypeError,
+                     "Can't instantiate abstract class %s "
+                     "with abstract methods %U",
+                     type->tp_name,
+                     joined);
+    error:
+        Py_XDECREF(joined);
+        Py_XDECREF(sorted_methods);
+        Py_XDECREF(abstract_methods);
+        return NULL;
+    }
+
+    size = _PyObject_VAR_SIZE(type, nitems+1);
     if (PyType_IS_GC(type))
         obj = _PyObject_GC_Malloc(size);
     else
@@ -2801,51 +2848,6 @@
     if (err < 0)
         return NULL;
 
-    if (type->tp_flags & Py_TPFLAGS_IS_ABSTRACT) {
-        static PyObject *comma = NULL;
-        PyObject *abstract_methods = NULL;
-        PyObject *builtins;
-        PyObject *sorted;
-        PyObject *sorted_methods = NULL;
-        PyObject *joined = NULL;
-
-        /* Compute ", ".join(sorted(type.__abstractmethods__))
-           into joined. */
-        abstract_methods = type_abstractmethods(type, NULL);
-        if (abstract_methods == NULL)
-            goto error;
-        builtins = PyEval_GetBuiltins();
-        if (builtins == NULL)
-            goto error;
-        sorted = PyDict_GetItemString(builtins, "sorted");
-        if (sorted == NULL)
-            goto error;
-        sorted_methods = PyObject_CallFunctionObjArgs(sorted,
-                                                      abstract_methods,
-                                                      NULL);
-        if (sorted_methods == NULL)
-            goto error;
-        if (comma == NULL) {
-            comma = PyUnicode_InternFromString(", ");
-            if (comma == NULL)
-                goto error;
-        }
-        joined = PyObject_CallMethod(comma, "join",
-                                     "O",  sorted_methods);
-        if (joined == NULL)
-            goto error;
-
-        PyErr_Format(PyExc_TypeError,
-                     "Can't instantiate abstract class %s "
-                     "with abstract methods %U",
-                     type->tp_name,
-                     joined);
-    error:
-        Py_XDECREF(joined);
-        Py_XDECREF(sorted_methods);
-        Py_XDECREF(abstract_methods);
-        return NULL;
-    }
     return type->tp_alloc(type, 0);
 }