diff --git a/Lib/os.py b/Lib/os.py
index 2e8ba921222..5c80e67eb4d 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -539,7 +539,7 @@ def getenvb(key, default=None):
 def _fscodec():
     encoding = sys.getfilesystemencoding()
     if encoding == 'mbcs':
-        errors = None   # strict
+        errors = 'strict'
     else:
         errors = 'surrogateescape'