--- libmalloc/libmalloc-409.40.6/src/purgeable_malloc.c
+++ libmalloc/libmalloc-521.100.59/src/purgeable_malloc.c
@@ -214,9 +214,7 @@
 	szone_t *szone;
 	kern_return_t err;
 
-	if (!reader) {
-		reader = _malloc_default_reader;
-	}
+	reader = reader_or_in_memory_fallback(reader, task);
 
 	err = reader(task, zone_address, sizeof(szone_t), (void **)&szone);
 	if (err) {