+++ b/src/lint/engine/ArcanistConfigurationDrivenLintEngine.php
@@ -35,6 +35,7 @@ final class ArcanistConfigurationDrivenLintEngine extends ArcanistLintEngine {
       PhutilTypeSpec::checkMap(
         $config,
         array(
+          '_comment' => 'optional string | list<string>',
           'exclude' => 'optional regex | list<regex>',
           'linters' => 'map<string, map<string, wild>>',
         ));