--- a/tests/test-hgweb-commands.t	Tue Sep 04 17:33:22 2018 +0300
+++ b/tests/test-hgweb-commands.t	Tue Sep 04 17:33:59 2018 +0300
@@ -26,7 +26,7 @@
   $ hg ci -Ambranch
   $ hg branch unstable
   marked working directory as branch unstable
-  >>> open('msg', 'wb').write('branch commit with null character: \0\n')
+  >>> open('msg', 'wb').write(b'branch commit with null character: \0\n')
   $ hg ci -l msg
   $ rm msg