lib/PublicInbox/LeiExternal.pm | 3 +++
 t/lei.t                        | 4 ++++

diff --git a/lib/PublicInbox/LeiExternal.pm b/lib/PublicInbox/LeiExternal.pm
index e7693e09a7de67a427742590707926352e54aed0..bf07c41cf7215e01d02cc0e3b949f6958184a816 100644
--- a/lib/PublicInbox/LeiExternal.pm
+++ b/lib/PublicInbox/LeiExternal.pm
@@ -58,6 +58,9 @@ 	my ($self, $location) = @_;
 	my $cfg = $self->_lei_cfg(1);
 	my $new_boost = $self->{opt}->{boost} // 0;
 	$location = _canonicalize($location);
+	if ($location !~ m!\Ahttps?://! && !-d $location) {
+		return $self->fail("$location not a directory");
+	}
 	my $key = "external.$location.boost";
 	my $cur_boost = $cfg->{$key};
 	return if defined($cur_boost) && $cur_boost == $new_boost; # idempotent
diff --git a/t/lei.t b/t/lei.t
index 6b45f5b7c34ec23e3483ee6b84a8fc6765198d83..60ca75c5da8084be83078b5679ac6176d3e0ed3f 100644
--- a/t/lei.t
+++ b/t/lei.t
@@ -193,6 +193,10 @@ 	is($out.$err, '', 'ls-external no output, yet');
 	ok(!-e $config_file && !-e $store_dir,
 		'nothing created by ls-external');
 
+	ok(!$lei->('add-external', "$home/nonexistent"),
+		"fails on non-existent dir");
+	$lei->('ls-external');
+	is($out.$err, '', 'ls-external still has no output');
 	my $cfg = PublicInbox::Config->new;
 	$cfg->each_inbox(sub {
 		my ($ibx) = @_;