diff -r 6858409f51bf Objects/structseq.c
--- a/Objects/structseq.c	Wed Dec 21 19:49:22 2011 +1300
+++ b/Objects/structseq.c	Fri Sep 14 22:21:06 2012 +0200
@@ -493,7 +493,18 @@
             n_unnamed_members++;
     n_members = i;
 
+#ifdef STACKLESS
+    if (PyType_HasFeature(type, Py_TPFLAGS_HAVE_STACKLESS_EXTENSION)) {
+        memcpy(type, &_struct_sequence_template, sizeof(PyTypeObject));
+    } else {
+        memcpy(type, &_struct_sequence_template, 
+               ((size_t) &(((PyTypeObject *)0)->as_number))  /* there should be a macro for this expression */
+        );
+        type->tp_flags &= ~Py_TPFLAGS_HAVE_STACKLESS_EXTENSION;
+    }
+#else
     memcpy(type, &_struct_sequence_template, sizeof(PyTypeObject));
+#endif
     type->tp_name = desc->name;
     type->tp_doc = desc->doc;
     type->tp_basicsize = sizeof(PyStructSequence)+