The array type was missing the Py_TPFLAGS_DEFAULT initializer for the
tp_flags. This will become important when I introduce
Py_TPFLAGS_HAVE_RICHCOMPARE (as I should have!).
diff --git a/Modules/arraymodule.c b/Modules/arraymodule.c
index f254359..374b3ac 100644
--- a/Modules/arraymodule.c
+++ b/Modules/arraymodule.c
@@ -1543,7 +1543,7 @@
0, /* tp_getattro */
0, /* tp_setattro */
&array_as_buffer, /* tp_as _buffer*/
- 0, /* tp_flags */
+ Py_TPFLAGS_DEFAULT, /* tp_flags */
arraytype_doc, /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */