diff -r b8184dbc9572 Objects/frameobject.c
--- a/Objects/frameobject.c	Thu Mar 22 02:17:35 2012 +0100
+++ b/Objects/frameobject.c	Thu Mar 22 02:35:10 2012 +0100
@@ -614,8 +614,6 @@ PyFrame_New(PyThreadState *tstate, PyCod
                 builtins = PyModule_GetDict(builtins);
                 assert(!builtins || PyDict_Check(builtins));
             }
-            else if (!PyDict_Check(builtins))
-                builtins = NULL;
         }
         if (builtins == NULL) {
             /* No builtins!              Make up a minimal one
@@ -634,7 +632,7 @@ PyFrame_New(PyThreadState *tstate, PyCod
         /* If we share the globals, we share the builtins.
            Save a lookup and a call. */
         builtins = back->f_builtins;
-        assert(builtins != NULL && PyDict_Check(builtins));
+        assert(builtins != NULL);
         Py_INCREF(builtins);
     }
     if (code->co_zombieframe != NULL) {
diff -r b8184dbc9572 Python/ceval.c
--- a/Python/ceval.c	Thu Mar 22 02:17:35 2012 +0100
+++ b/Python/ceval.c	Thu Mar 22 02:35:10 2012 +0100
@@ -1930,7 +1930,15 @@ PyEval_EvalFrameEx(PyFrameObject *f, int
         TARGET(LOAD_BUILD_CLASS)
         {
             _Py_IDENTIFIER(__build_class__);
-            x = _PyDict_GetItemId(f->f_builtins, &PyId___build_class__);
+
+            if (PyDict_CheckExact(f->f_builtins))
+                x = _PyDict_GetItemId(f->f_builtins, &PyId___build_class__);
+            else {
+                PyObject *build_class_str = _PyUnicode_FromId(&PyId___build_class__);
+                if (build_class_str == NULL)
+                    break;
+                x = PyObject_GetItem(f->f_builtins, build_class_str);
+            }
             if (x == NULL) {
                 PyErr_SetString(PyExc_ImportError,
                                 "__build_class__ not found");
@@ -2076,7 +2084,10 @@ PyEval_EvalFrameEx(PyFrameObject *f, int
             if (x == NULL) {
                 x = PyDict_GetItem(f->f_globals, w);
                 if (x == NULL) {
-                    x = PyDict_GetItem(f->f_builtins, w);
+                    if (PyDict_CheckExact(f->f_builtins))
+                        x = PyDict_GetItem(f->f_builtins, w);
+                    else
+                        x = PyObject_GetItem(f->f_builtins, w);
                     if (x == NULL) {
                         format_exc_check_arg(
                                     PyExc_NameError,
@@ -2091,7 +2102,9 @@ PyEval_EvalFrameEx(PyFrameObject *f, int
 
         TARGET(LOAD_GLOBAL)
             w = GETITEM(names, oparg);
-            if (PyUnicode_CheckExact(w)) {
+            if (PyDict_CheckExact(f->f_globals)
+                && PyDict_CheckExact(f->f_builtins)
+                && PyUnicode_CheckExact(w)) {
                 /* Inline the PyDict_GetItem() calls.
                    WARNING: this is an extreme speed hack.
                    Do not try this at home. */
@@ -2123,21 +2136,25 @@ PyEval_EvalFrameEx(PyFrameObject *f, int
                         PUSH(x);
                         DISPATCH();
                     }
-                    goto load_global_error;
-                }
-            }
-            /* This is the un-inlined version of the code above */
-            x = PyDict_GetItem(f->f_globals, w);
-            if (x == NULL) {
-                x = PyDict_GetItem(f->f_builtins, w);
-                if (x == NULL) {
-                  load_global_error:
                     format_exc_check_arg(
                                 PyExc_NameError,
                                 GLOBAL_NAME_ERROR_MSG, w);
                     break;
                 }
             }
+            else {
+                /* This is the un-inlined version of the code above */
+                x = PyDict_GetItem(f->f_globals, w);
+                if (x == NULL) {
+                    x = PyDict_GetItem(f->f_builtins, w);
+                    if (x == NULL) {
+                        format_exc_check_arg(
+                                    PyExc_NameError,
+                                    GLOBAL_NAME_ERROR_MSG, w);
+                        break;
+                    }
+                }
+            }
             Py_INCREF(x);
             PUSH(x);
             DISPATCH();