die "Only conversion from v1 inboxes is supported\n" if $old->version >= 2;
require PublicInbox::Admin;
-$old->{indexlevel} //= PublicInbox::Admin::detect_indexlevel($old);
+my $detected = PublicInbox::Admin::detect_indexlevel($old);
+$old->{indexlevel} //= $detected;
my $env;
if ($opt->{'index'}) {
my $mods = {};