diff --git a/Lib/_osx_support.py b/Lib/_osx_support.py
index eadf06f..e37852e 100644
--- a/Lib/_osx_support.py
+++ b/Lib/_osx_support.py
@@ -210,7 +210,7 @@
         # Do not alter a config var explicitly overridden by env var
         if cv in _config_vars and cv not in os.environ:
             flags = _config_vars[cv]
-            flags = re.sub(r'-arch\s+\w+\s', ' ', flags, re.ASCII)
+            flags = re.sub(r'-arch\s+\w+\s', ' ', flags, flags=re.ASCII)
             flags = re.sub('-isysroot [^ \t]*', ' ', flags)
             _save_modified_value(_config_vars, cv, flags)