--- a/mercurial/mail.py	Mon Jan 06 01:37:43 2025 -0500
+++ b/mercurial/mail.py	Mon Jan 06 01:39:53 2025 -0500
@@ -519,7 +519,7 @@
                 pass
         # On Python 3, decode_header() may return either bytes or unicode
         # depending on whether the header has =?<charset>? or not
-        if isinstance(part, type(u'')):
+        if isinstance(part, str):
             uparts.append(part)
             continue
         try: