diff -r 6b52cffd8d0a -r e2f7b2695ba1 mercurial/merge.py
--- a/mercurial/merge.py	Tue Mar 02 00:05:22 2021 +0100
+++ b/mercurial/merge.py	Thu Mar 18 18:24:59 2021 -0400
@@ -20,6 +20,7 @@
     nullrev,
 )
 from .thirdparty import attr
+from .utils import stringutil
 from . import (
     copies,
     encoding,
@@ -1343,7 +1344,7 @@
         except OSError as inst:
             repo.ui.warn(
                 _(b"update failed to remove %s: %s!\n")
-                % (f, pycompat.bytestr(inst.strerror))
+                % (f, stringutil.forcebytestr(inst.strerror))
             )
         if i == 100:
             yield i, f