diff --git a/src/infrastructure/env/PhabricatorEnv.php b/src/infrastructure/env/PhabricatorEnv.php
--- a/src/infrastructure/env/PhabricatorEnv.php
+++ b/src/infrastructure/env/PhabricatorEnv.php
@@ -433,7 +433,7 @@
 
     $host = $uri->getDomain();
     if (!phutil_nonempty_string($host)) {
-      return false;
+      return true;
     }
 
     $host = phutil_utf8_strtolower($host);
diff --git a/src/infrastructure/env/__tests__/PhabricatorEnvTestCase.php b/src/infrastructure/env/__tests__/PhabricatorEnvTestCase.php
--- a/src/infrastructure/env/__tests__/PhabricatorEnvTestCase.php
+++ b/src/infrastructure/env/__tests__/PhabricatorEnvTestCase.php
@@ -243,6 +243,12 @@
       'https://old.example.com/path/to/resource.png' => true,
 
       'https://other.example.com/' => false,
+
+      '/' => true,
+      '/self' => true,
+      '#self' => true,
+      '/#self' => true,
+      '/self/#self' => true,
     );
 
     foreach ($map as $input => $expect) {