diff --git a/mercurial/crecord.py b/mercurial/crecord.py
--- a/mercurial/crecord.py
+++ b/mercurial/crecord.py
@@ -1799,6 +1799,7 @@
                 break
 
         if self.commenttext != "":
-            whitespaceremoved = re.sub("(?m)^\s.*(\n|$)", "", self.commenttext)
+            whitespaceremoved = re.sub(br"(?m)^\s.*(\n|$)", b"",
+                                       self.commenttext)
             if whitespaceremoved != "":
                 self.opts['message'] = self.commenttext