diff -r 2372284d9457 -r 687b865b95ad mercurial/revlogutils/sidedata.py
--- a/mercurial/revlogutils/sidedata.py	Sun Oct 06 09:45:02 2019 -0400
+++ b/mercurial/revlogutils/sidedata.py	Sun Oct 06 09:48:39 2019 -0400
@@ -63,7 +63,7 @@
     for key, value in sidedata:
         rawtext.append(value)
     rawtext.append(bytes(text))
-    return ''.join(rawtext), False
+    return b''.join(rawtext), False
 
 
 def sidedatareadprocessor(rl, text):