lib/PublicInbox/Config.pm | 4 ++++

diff --git a/lib/PublicInbox/Config.pm b/lib/PublicInbox/Config.pm
index 228de4ffe88f631fbccbaee594087a8680adcafd..26ac298eddb86f2256c4618d7abef920f7a4b95d 100644
--- a/lib/PublicInbox/Config.pm
+++ b/lib/PublicInbox/Config.pm
@@ -510,6 +510,10 @@ 	eval { require PublicInbox::ExtSearch } or return;
 	my $pfx = "extindex.$name";
 	my $d = $self->{"$pfx.topdir"} // return;
 	-d $d or return;
+	if (index($d, "\n") >= 0) {
+		warn "E: `$d' must not contain `\\n'\n";
+		return;
+	}
 	my $es = PublicInbox::ExtSearch->new($d);
 	for my $k (qw(indexlevel indexsequentialshard)) {
 		my $v = _one_val($self, $pfx, $k) // next;