diff --git a/Python/getargs.c b/Python/getargs.c
index 7c3e9fa..02351ed 100644
--- a/Python/getargs.c
+++ b/Python/getargs.c
@@ -984,10 +984,11 @@
             if (*format == '#') {
                 FETCH_SIZE;
                 assert(0); /* XXX redundant with if-case */
-                if (arg == Py_None)
-                    *q = 0;
-                else
-                    *q = PyString_Size(arg);
+                if (arg == Py_None) {
+                    STORE_SIZE(0);
+                } else {
+                    STORE_SIZE(PyString_Size(arg));
+                }
                 format++;
             }
             else if (*p != NULL &&