diff --git a/core/tests/bootstrap.php b/core/tests/bootstrap.php
index 65679fe..00bea46 100644
--- a/core/tests/bootstrap.php
+++ b/core/tests/bootstrap.php
@@ -21,7 +21,7 @@ function drupal_phpunit_find_extension_directories($scan_directory) {
   $dir = new \RecursiveIteratorIterator(new \RecursiveDirectoryIterator($scan_directory, \RecursiveDirectoryIterator::FOLLOW_SYMLINKS));
   foreach ($dir as $d) {
     if (strpos($d->getPathname(), 'info.yml') !== FALSE) {
-      // Cut off ".info.yml" from the filename to be used as the extension name.
+      // Cut off ".info.yml" from the filename for use as the extension name.
       $extensions[substr($d->getFilename(), 0, -9)] = $d->getPathInfo()->getRealPath();
     }
   }
@@ -38,11 +38,10 @@ function drupal_phpunit_find_extension_directories($scan_directory) {
 function drupal_phpunit_contrib_extension_directory_roots() {
   $sites_path = __DIR__ . '/../../sites';
   $paths = array();
-  // Note this also checks sites/../modules, themes, and profiles.
+  // Note this also checks sites/../modules and sites/../profiles.
   foreach (scandir($sites_path) as $site) {
     $path = "$sites_path/$site";
     $paths[] = is_dir("$path/modules") ? realpath("$path/modules") : NULL;
-    $paths[] = is_dir("$path/themes") ? realpath("$path/themes") : NULL;
     $paths[] = is_dir("$path/profiles") ? realpath("$path/profiles") : NULL;
   }
   return array_filter($paths);
@@ -78,7 +77,6 @@ function drupal_phpunit_register_extension_dirs(Composer\Autoload\ClassLoader $l
 // Scan for arbitrary extension namespaces from core and contrib.
 $extension_roots = array_merge(array(
   __DIR__ . '/../modules',
-  __DIR__ . '/../themes',
   __DIR__ . '/../profiles',
 ), drupal_phpunit_contrib_extension_directory_roots());