diff --git a/includes/path.inc b/includes/path.inc
index db60537..804345e 100644
--- a/includes/path.inc
+++ b/includes/path.inc
@@ -55,21 +55,13 @@ function drupal_lookup_path($action, $path = '', $path_language = NULL) {
     $cache = array(
       'map' => array(),
       'no_source' => array(),
-      'whitelist' => NULL,
+      'whitelist' => new PathAliasWhitelist('path_alias_whitelist', 'cache'),
       'system_paths' => array(),
       'no_aliases' => array(),
       'first_call' => TRUE,
     );
   }
 
-  // Retrieve the path alias whitelist.
-  if (!isset($cache['whitelist'])) {
-    $cache['whitelist'] = variable_get('path_alias_whitelist', NULL);
-    if (!isset($cache['whitelist'])) {
-      $cache['whitelist'] = drupal_path_alias_whitelist_rebuild();
-    }
-  }
-
   // If no language is explicitly specified we default to the current URL
   // language. If we used a language different from the one conveyed by the
   // requested URL, we might end up being unable to check if there is a path
@@ -356,33 +348,40 @@ function current_path() {
 }
 
 /**
+ * Extends DrupalCacheArray to build the path alias whitelist over time.
+ */ 
+class PathAliasWhitelist extends DrupalCacheArray {
+  function resolveCacheMiss($offset) {
+    $exists = (bool) db_query_range('SELECT 1 FROM {url_alias} WHERE source LIKE :path', 0, 1, array(':path' => $offset . '%'))->fetchField();
+    // If a path prefix does not exist, store it as NULL rather than FALSE
+    // since DrupalCacheArray uses isset() in offsetExists().
+    $value = $exists ? TRUE : NULL;
+    $this->storage[$offset] = $value;
+    $this->persist($offset);
+    return $value;
+  }
+}
+
+/**
  * Rebuild the path alias white list.
  *
  * @param $source
  *   An optional system path for which an alias is being inserted.
  *
  * @return
- *   An array containing a white list of path aliases.
+ *   An instance of the PathAliasWhitelist class.
  */
 function drupal_path_alias_whitelist_rebuild($source = NULL) {
   // When paths are inserted, only rebuild the whitelist if the system path
   // has a top level component which is not already in the whitelist.
   if (!empty($source)) {
-    $whitelist = variable_get('path_alias_whitelist', NULL);
+    $whitelist = new PathAliasWhitelist('path_alias_whitelist', 'cache');
     if (isset($whitelist[strtok($source, '/')])) {
       return $whitelist;
     }
   }
-  // For each alias in the database, get the top level component of the system
-  // path it corresponds to. This is the portion of the path before the first
-  // '/', if present, otherwise the whole path itself.
-  $whitelist = array();
-  $result = db_query("SELECT DISTINCT SUBSTRING_INDEX(source, '/', 1) AS path FROM {url_alias}");
-  foreach ($result as $row) {
-    $whitelist[$row->path] = TRUE;
-  }
-  variable_set('path_alias_whitelist', $whitelist);
-  return $whitelist;
+  cache_clear_all('path_alias_whitelist', 'cache');
+  return new PathAliasWhitelist('path_alias_whitelist', 'cache');
 }
 
 /**
diff --git a/modules/simpletest/drupal_web_test_case.php b/modules/simpletest/drupal_web_test_case.php
index 5c39cfc..b2a7bf1 100644
--- a/modules/simpletest/drupal_web_test_case.php
+++ b/modules/simpletest/drupal_web_test_case.php
@@ -1238,6 +1238,10 @@ class DrupalWebTestCase extends DrupalTestCase {
       ->condition('test_id', $this->testId)
       ->execute();
 
+    // Reset all statics and variables to perform tests in a clean environment.
+    $conf = array();
+    drupal_static_reset();
+
     // Clone the current connection and replace the current prefix.
     $connection_info = Database::getConnectionInfo('default');
     Database::renameConnection('default', 'simpletest_original_default');
@@ -1285,10 +1289,6 @@ class DrupalWebTestCase extends DrupalTestCase {
     ini_set('log_errors', 1);
     ini_set('error_log', $public_files_directory . '/error.log');
 
-    // Reset all statics and variables to perform tests in a clean environment.
-    $conf = array();
-    drupal_static_reset();
-
     // Set the test information for use in other parts of Drupal.
     $test_info = &$GLOBALS['drupal_test_info'];
     $test_info['test_run_id'] = $this->databasePrefix;
diff --git a/modules/simpletest/tests/theme.test b/modules/simpletest/tests/theme.test
index f1e1bd5..2529e8d 100644
--- a/modules/simpletest/tests/theme.test
+++ b/modules/simpletest/tests/theme.test
@@ -194,7 +194,7 @@ class ThemeItemListUnitTest extends DrupalWebTestCase {
 /**
  * Unit tests for theme_links().
  */
-class ThemeLinksUnitTest extends DrupalUnitTestCase {
+class ThemeLinksTest extends DrupalWebTestCase {
   public static function getInfo() {
     return array(
       'name' => 'Links',