diff --git a/core/includes/tablesort.inc b/core/includes/tablesort.inc
index a900a612fe73..818b61d1b562 100644
--- a/core/includes/tablesort.inc
+++ b/core/includes/tablesort.inc
@@ -12,101 +12,6 @@ use Drupal\Core\Database\Query\SelectInterface;
  * column headers that the user can click on to sort the table by that column.
  */
 
-/**
- * Query extender class for tablesort queries.
- */
-class TableSort extends SelectExtender {
-
-  /**
-   * The array of fields that can be sorted by.
-   *
-   * @var array
-   */
-  protected $header = array();
-
-  public function __construct(SelectInterface $query, Connection $connection) {
-    parent::__construct($query, $connection);
-
-    // Add convenience tag to mark that this is an extended query. We have to
-    // do this in the constructor to ensure that it is set before preExecute()
-    // gets called.
-    $this->addTag('tablesort');
-  }
-
-  /**
-   * Order the query based on a header array.
-   *
-   * @see theme_table()
-   * @param $header
-   *   Table header array.
-   * @return SelectQueryInterface
-   *   The called object.
-   */
-  public function orderByHeader(Array $header) {
-    $this->header = $header;
-    $ts = $this->init();
-    if (!empty($ts['sql'])) {
-      // Based on code from db_escape_table(), but this can also contain a dot.
-      $field = preg_replace('/[^A-Za-z0-9_.]+/', '', $ts['sql']);
-
-      // Sort order can only be ASC or DESC.
-      $sort = drupal_strtoupper($ts['sort']);
-      $sort = in_array($sort, array('ASC', 'DESC')) ? $sort : '';
-      $this->orderBy($field, $sort);
-    }
-    return $this;
-  }
-
-  /**
-   * Initialize the table sort context.
-   */
-  protected function init() {
-    $ts = $this->order();
-    $ts['sort'] = $this->getSort();
-    $ts['query'] = $this->getQueryParameters();
-    return $ts;
-  }
-
-  /**
-   * Determine the current sort direction.
-   *
-   * @param $headers
-   *   An array of column headers in the format described in theme_table().
-   * @return
-   *   The current sort direction ("asc" or "desc").
-   */
-  protected function getSort() {
-    return tablesort_get_sort($this->header);
-  }
-
-  /**
-   * Compose a URL query parameter array to append to table sorting requests.
-   *
-   * @return
-   *   A URL query parameter array that consists of all components of the current
-   *   page request except for those pertaining to table sorting.
-   *
-   * @see tablesort_get_query_parameters()
-   */
-  protected function getQueryParameters() {
-    return tablesort_get_query_parameters();
-  }
-
-  /**
-   * Determine the current sort criterion.
-   *
-   * @param $headers
-   *   An array of column headers in the format described in theme_table().
-   * @return
-   *   An associative array describing the criterion, containing the keys:
-   *   - "name": The localized title of the table column.
-   *   - "sql": The name of the database field to sort on.
-   */
-  protected function order() {
-    return tablesort_get_order($this->header);
-  }
-}
-
 /**
  * Initialize the table sort context.
  */
diff --git a/core/lib/Drupal/Core/Database/Query/TableSortExtender.php b/core/lib/Drupal/Core/Database/Query/TableSortExtender.php
new file mode 100644
index 000000000000..cf1a0420cc17
--- /dev/null
+++ b/core/lib/Drupal/Core/Database/Query/TableSortExtender.php
@@ -0,0 +1,105 @@
+<?php
+
+/**
+ * @file
+ * Definition of Drupal\Core\Database\Query\TableSortExtender.
+ */
+
+namespace Drupal\Core\Database\Query;
+
+use Drupal\Core\Database\Connection;
+
+/**
+ * Query extender class for tablesort queries.
+ */
+class TableSortExtender extends SelectExtender {
+
+  /**
+   * The array of fields that can be sorted by.
+   */
+  protected $header = array();
+
+  public function __construct(SelectInterface $query, Connection $connection) {
+    parent::__construct($query, $connection);
+
+    // Add convenience tag to mark that this is an extended query. We have to
+    // do this in the constructor to ensure that it is set before preExecute()
+    // gets called.
+    $this->addTag('tablesort');
+  }
+
+  /**
+   * Order the query based on a header array.
+   *
+   * @param array $header
+   *   Table header array.
+   *
+   * @return SelectQueryInterface
+   *   The called object.
+   *
+   * @see theme_table()
+   */
+  public function orderByHeader(array $header) {
+    $this->header = $header;
+    $ts = $this->init();
+    if (!empty($ts['sql'])) {
+      // Based on code from db_escape_table(), but this can also contain a dot.
+      $field = preg_replace('/[^A-Za-z0-9_.]+/', '', $ts['sql']);
+
+      // Sort order can only be ASC or DESC.
+      $sort = drupal_strtoupper($ts['sort']);
+      $sort = in_array($sort, array('ASC', 'DESC')) ? $sort : '';
+      $this->orderBy($field, $sort);
+    }
+    return $this;
+  }
+
+  /**
+   * Initialize the table sort context.
+   */
+  protected function init() {
+    $ts = $this->order();
+    $ts['sort'] = $this->getSort();
+    $ts['query'] = $this->getQueryParameters();
+    return $ts;
+  }
+
+  /**
+   * Determine the current sort direction.
+   *
+   * @return
+   *   The current sort direction ("asc" or "desc").
+   *
+   * @see tablesort_get_sort()
+   */
+  protected function getSort() {
+    return tablesort_get_sort($this->header);
+  }
+
+  /**
+   * Compose a URL query parameter array to append to table sorting requests.
+   *
+   * @return
+   *   A URL query parameter array that consists of all components of the current
+   *   page request except for those pertaining to table sorting.
+   *
+   * @see tablesort_get_query_parameters()
+   */
+  protected function getQueryParameters() {
+    return tablesort_get_query_parameters();
+  }
+
+  /**
+   * Determine the current sort criterion.
+   *
+   * @return
+   *   An associative array describing the criterion, containing the keys:
+   *   - "name": The localized title of the table column.
+   *   - "sql": The name of the database field to sort on.
+   *
+   * @see tablesort_get_order()
+   */
+  protected function order() {
+    return tablesort_get_order($this->header);
+  }
+}
diff --git a/core/modules/comment/comment.admin.inc b/core/modules/comment/comment.admin.inc
index 3a853df6a814..bec68c56e1e7 100644
--- a/core/modules/comment/comment.admin.inc
+++ b/core/modules/comment/comment.admin.inc
@@ -81,7 +81,7 @@ function comment_admin_overview($form, &$form_state, $arg) {
 
   $query = db_select('comment', 'c')
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   $query->join('node', 'n', 'n.nid = c.nid');
   $query->addField('n', 'title', 'node_title');
   $query->addTag('node_access');
diff --git a/core/modules/dblog/dblog.admin.inc b/core/modules/dblog/dblog.admin.inc
index dafc91b021ce..7c04b6ca0065 100644
--- a/core/modules/dblog/dblog.admin.inc
+++ b/core/modules/dblog/dblog.admin.inc
@@ -39,7 +39,7 @@ function dblog_overview() {
 
   $query = db_select('watchdog', 'w')
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   $query->leftJoin('users', 'u', 'w.uid = u.uid');
   $query
     ->fields('w', array('wid', 'uid', 'severity', 'type', 'timestamp', 'message', 'variables', 'link'))
@@ -100,7 +100,7 @@ function dblog_top($type) {
 
   $query = db_select('watchdog', 'w')
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   $query->addExpression('COUNT(wid)', 'count');
   $query = $query
     ->fields('w', array('message', 'variables'))
diff --git a/core/modules/forum/forum.module b/core/modules/forum/forum.module
index 25a4369363af..2f170426e255 100644
--- a/core/modules/forum/forum.module
+++ b/core/modules/forum/forum.module
@@ -895,7 +895,7 @@ function forum_get_topics($tid, $sortby, $forum_per_page) {
 
   $query = db_select('forum_index', 'f')
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   $query->fields('f');
   $query
     ->condition('f.tid', $tid)
@@ -918,7 +918,8 @@ function forum_get_topics($tid, $sortby, $forum_per_page) {
   if ($nids) {
     $nodes = node_load_multiple($nids);
 
-    $query = db_select('node', 'n')->extend('TableSort');
+    $query = db_select('node', 'n')
+      ->extend('Drupal\Core\Database\Query\TableSortExtender');
     $query->fields('n', array('nid'));
 
     $query->join('node_comment_statistics', 'ncs', 'n.nid = ncs.nid');
diff --git a/core/modules/node/node.admin.inc b/core/modules/node/node.admin.inc
index c933daaa2dc1..fc8d98a9eff8 100644
--- a/core/modules/node/node.admin.inc
+++ b/core/modules/node/node.admin.inc
@@ -449,7 +449,7 @@ function node_admin_nodes() {
 
   $query = db_select('node', 'n')
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   node_build_filter_query($query);
 
   if (!user_access('bypass node access')) {
diff --git a/core/modules/path/path.admin.inc b/core/modules/path/path.admin.inc
index a884f9eaeaf8..4188effed9ae 100644
--- a/core/modules/path/path.admin.inc
+++ b/core/modules/path/path.admin.inc
@@ -29,7 +29,7 @@ function path_admin_overview($keys = NULL) {
 
   $query = db_select('url_alias')
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   if ($keys) {
     // Replace wildcards with PDO wildcards.
     $query->condition('alias', '%' . preg_replace('!\*+!', '%', $keys) . '%', 'LIKE');
diff --git a/core/modules/poll/poll.pages.inc b/core/modules/poll/poll.pages.inc
index b04f99ccb051..732355de3e7f 100644
--- a/core/modules/poll/poll.pages.inc
+++ b/core/modules/poll/poll.pages.inc
@@ -58,7 +58,7 @@ function poll_votes($node) {
 
   $select = db_select('poll_vote', 'pv')
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   $select->join('poll_choice', 'pc', 'pv.chid = pc.chid');
   $select->join('users', 'u', 'pv.uid = u.uid');
   $queried_votes = $select
diff --git a/core/modules/statistics/statistics.admin.inc b/core/modules/statistics/statistics.admin.inc
index 84bf60d93ade..d84e07bc6c66 100644
--- a/core/modules/statistics/statistics.admin.inc
+++ b/core/modules/statistics/statistics.admin.inc
@@ -27,7 +27,7 @@ function statistics_recent_hits() {
 
   $query = db_select('accesslog', 'a', array('target' => 'slave'))
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   $query->join('users', 'u', 'a.uid = u.uid');
   $query
     ->fields('a', array('aid', 'timestamp', 'path', 'title', 'uid'))
@@ -75,7 +75,7 @@ function statistics_top_pages() {
 
   $query = db_select('accesslog', 'a', array('target' => 'slave'))
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   $query->addExpression('COUNT(path)', 'hits');
   // MAX(title) avoids having empty node titles which otherwise causes
   // duplicates in the top pages list.
@@ -130,7 +130,7 @@ function statistics_top_visitors() {
   );
   $query = db_select('accesslog', 'a', array('target' => 'slave'))
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   $query->leftJoin('blocked_ips', 'bl', 'a.hostname = bl.ip');
   $query->leftJoin('users', 'u', 'a.uid = u.uid');
 
@@ -192,7 +192,7 @@ function statistics_top_referrers() {
   );
   $query = db_select('accesslog', 'a')
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
 
   $query->addExpression('COUNT(url)', 'hits');
   $query->addExpression('MAX(timestamp)', 'last');
diff --git a/core/modules/statistics/statistics.pages.inc b/core/modules/statistics/statistics.pages.inc
index 524d59e51e79..90383bbc1e04 100644
--- a/core/modules/statistics/statistics.pages.inc
+++ b/core/modules/statistics/statistics.pages.inc
@@ -27,7 +27,7 @@ function statistics_node_tracker() {
 
     $query = db_select('accesslog', 'a', array('target' => 'slave'))
       ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-      ->extend('TableSort');
+      ->extend('Drupal\Core\Database\Query\TableSortExtender');
     $query->join('users', 'u', 'a.uid = u.uid');
 
     $query
@@ -83,7 +83,7 @@ function statistics_user_tracker() {
         array('data' => t('Operations')));
     $query = db_select('accesslog', 'a', array('target' => 'slave'))
       ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-      ->extend('TableSort');
+      ->extend('Drupal\Core\Database\Query\TableSortExtender');
     $query
       ->fields('a', array('aid', 'timestamp', 'path', 'title'))
       ->condition('uid', $account->uid)
diff --git a/core/modules/system/tests/tablesort.test b/core/modules/system/lib/Drupal/system/Tests/Common/TableSortExtenderUnitTest.php
similarity index 96%
rename from core/modules/system/tests/tablesort.test
rename to core/modules/system/lib/Drupal/system/Tests/Common/TableSortExtenderUnitTest.php
index 1dc35fee6577..dbb7d7b49370 100644
--- a/core/modules/system/tests/tablesort.test
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/TableSortExtenderUnitTest.php
@@ -2,15 +2,17 @@
 
 /**
  * @file
- * Various tablesort tests.
+ * Definition of Drupal\system\Tests\Common\TableSortExtenderTest.
  */
 
+namespace Drupal\system\Tests\Common;
+
 use Drupal\simpletest\UnitTestBase;
 
 /**
  * Test unicode handling features implemented in unicode.inc.
  */
-class TableSortTest extends UnitTestBase {
+class TableSortExtenderUnitTest extends UnitTestBase {
 
   /**
    * Storage for initial value of $_GET.
diff --git a/core/modules/system/system.admin.inc b/core/modules/system/system.admin.inc
index 9c682f0ae93f..f34c766b0bc9 100644
--- a/core/modules/system/system.admin.inc
+++ b/core/modules/system/system.admin.inc
@@ -2924,7 +2924,7 @@ function system_actions_manage() {
   );
   $query = db_select('actions')
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   $result = $query
     ->fields('actions')
     ->limit(50)
diff --git a/core/modules/system/tests/modules/database_test/database_test.module b/core/modules/system/tests/modules/database_test/database_test.module
index f248e5a00820..4500f741af50 100644
--- a/core/modules/system/tests/modules/database_test/database_test.module
+++ b/core/modules/system/tests/modules/database_test/database_test.module
@@ -161,7 +161,9 @@ function database_test_tablesort() {
   $query
     ->fields('t', array('tid', 'pid', 'task', 'priority'));
 
-  $query = $query->extend('TableSort')->orderByHeader($header);
+  $query = $query
+    ->extend('Drupal\Core\Database\Query\TableSortExtender')
+    ->orderByHeader($header);
 
   // We need all the results at once to check the sort.
   $tasks = $query->execute()->fetchAll();
@@ -190,7 +192,10 @@ function database_test_tablesort_first() {
   $query
     ->fields('t', array('tid', 'pid', 'task', 'priority'));
 
-  $query = $query->extend('TableSort')->orderByHeader($header)->orderBy('priority');
+  $query = $query
+    ->extend('Drupal\Core\Database\Query\TableSortExtender')
+    ->orderByHeader($header)
+    ->orderBy('priority');
 
   // We need all the results at once to check the sort.
   $tasks = $query->execute()->fetchAll();
diff --git a/core/modules/user/user.admin.inc b/core/modules/user/user.admin.inc
index 9f3108c14935..be75907648f4 100644
--- a/core/modules/user/user.admin.inc
+++ b/core/modules/user/user.admin.inc
@@ -160,7 +160,7 @@ function user_admin_account() {
 
   $query = $query
     ->extend('Drupal\Core\Database\Query\PagerSelectExtender')
-    ->extend('TableSort');
+    ->extend('Drupal\Core\Database\Query\TableSortExtender');
   $query
     ->fields('u', array('uid', 'name', 'status', 'created', 'access'))
     ->limit(50)