diff --git a/arcanist/lib/WatchmanLintEngine.php b/arcanist/lib/WatchmanLintEngine.php
index <HASH>..<HASH> 100644
--- a/arcanist/lib/WatchmanLintEngine.php
+++ b/arcanist/lib/WatchmanLintEngine.php
@@ -4,6 +4,10 @@
 
 class WatchmanLintEngine extends ArcanistLintEngine {
 
+  private static $IGNORED_PATH_PATTERNS = array(
+    '%^thirdparty/%',
+  );
+
   public function buildLinters() {
     $linters = array();
     $paths = $this->getPaths();
@@ -13,6 +17,13 @@ class WatchmanLintEngine extends ArcanistLintEngine {
     foreach ($paths as $key => $path) {
       if (!Filesystem::pathExists($this->getFilePathOnDisk($path))) {
         unset($paths[$key]);
+      } else {
+        foreach (static::$IGNORED_PATH_PATTERNS as $pattern) {
+          if (preg_match($pattern, $path)) {
+            unset($paths[$key]);
+            break;
+          }
+        }
       }
     }
Don't run lint on thirdparty directories

Summary:
I'm going to import `wildmatch.c` into `thirdparty`,
but `arc lint` complains about its style.

This disables the lint engine on changes to `thirdparty`.

Test Plan: `arc lint` with `wildmatch.c` in `thirdparty`

Reviewers: wez

Differential Revision: <URL>