diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 86fdf27..13600c2 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -326,7 +326,7 @@
     if dev_mode:
         args.extend(('-X', 'dev'))
     for opt in ('faulthandler', 'tracemalloc', 'importtime',
-                'showrefcount', 'utf8'):
+                'showrefcount', 'utf8', 'oldparser'):
         if opt in xoptions:
             value = xoptions[opt]
             if value is True: