--- a/mercurial/util.py	Wed Mar 10 18:24:23 2021 +0100
+++ b/mercurial/util.py	Fri Mar 12 13:13:13 2021 -0500
@@ -2185,7 +2185,7 @@
         global _re2
         try:
             # check if match works, see issue3964
-            _re2 = bool(re2.match(r'\[([^\[]+)\]', b'[ui]'))
+            _re2 = bool(re2.match(br'\[([^\[]+)\]', b'[ui]'))
         except ImportError:
             _re2 = False