Issue #8268: Old-style classes (not just instances) now support weak
references.
diff --git a/Include/classobject.h b/Include/classobject.h
index 118dd09..bc03e0d 100644
--- a/Include/classobject.h
+++ b/Include/classobject.h
@@ -18,6 +18,7 @@
     PyObject	*cl_getattr;
     PyObject	*cl_setattr;
     PyObject	*cl_delattr;
+    PyObject    *cl_weakreflist; /* List of weak references */
 } PyClassObject;
 
 typedef struct {