diff --git a/phpBB/config/default/container/services_mention.yml b/phpBB/config/default/container/services_mention.yml
index 06c94d54b3..310bfce6a4 100644
--- a/phpBB/config/default/container/services_mention.yml
+++ b/phpBB/config/default/container/services_mention.yml
@@ -16,33 +16,17 @@ services:
         tags:
             - { name: service_collection, tag: mention.source }
 
-    phpbb.mention.source.friend:
-        class: phpbb\mention\source\friend
-        parent: phpbb.mention.source.user
-        calls:
-            - [set_user, ['@user']]
-        tags:
-            - { name: mention.source }
+    phpbb.mention.source.base_group:
+        abstract: true
+        arguments:
+            - '@dbal.conn'
+            - '@group_helper'
+            - '@user'
+            - '@auth'
+            - '%core.root_path%'
+            - '%core.php_ext%'
 
-    phpbb.mention.source.member:
-        class: phpbb\mention\source\member
-        parent: phpbb.mention.source.user
-        tags:
-            - { name: mention.source }
-
-    phpbb.mention.source.team:
-        class: phpbb\mention\source\team
-        parent: phpbb.mention.source.user
-        tags:
-            - { name: mention.source }
-
-    phpbb.mention.source.topic:
-        class: phpbb\mention\source\topic
-        parent: phpbb.mention.source.user
-        tags:
-            - { name: mention.source }
-
-    phpbb.mention.source.user:
+    phpbb.mention.source.base_user:
         abstract: true
         arguments:
             - '@dbal.conn'
@@ -50,13 +34,40 @@ services:
             - '%core.root_path%'
             - '%core.php_ext%'
 
-    phpbb.mention.source.usergroup:
-        class: phpbb\mention\source\usergroup
-        arguments:
-            - '@dbal.conn'
-            - '@group_helper'
-            - '@user'
-            - '%core.root_path%'
-            - '%core.php_ext%'
+    phpbb.mention.source.friend:
+        class: phpbb\mention\source\friend
+        parent: phpbb.mention.source.base_user
+        calls:
+            - [set_user, ['@user']]
+        tags:
+            - { name: mention.source }
+
+    phpbb.mention.source.group:
+        class: phpbb\mention\source\group
+        parent: phpbb.mention.source.base_group
+        tags:
+            - { name: mention.source }
+
+    phpbb.mention.source.team:
+        class: phpbb\mention\source\team
+        parent: phpbb.mention.source.base_user
+        tags:
+            - { name: mention.source }
+
+    phpbb.mention.source.topic:
+        class: phpbb\mention\source\topic
+        parent: phpbb.mention.source.base_user
+        tags:
+            - { name: mention.source }
+
+    phpbb.mention.source.user:
+        class: phpbb\mention\source\user
+        parent: phpbb.mention.source.base_user
+        tags:
+            - { name: mention.source }
+
+    phpbb.mention.source.usergroup:
+        class: phpbb\mention\source\usergroup
+        parent: phpbb.mention.source.base_group
         tags:
             - { name: mention.source }
diff --git a/phpBB/phpbb/mention/source/base_group.php b/phpBB/phpbb/mention/source/base_group.php
new file mode 100644
index 0000000000..47784835d7
--- /dev/null
+++ b/phpBB/phpbb/mention/source/base_group.php
@@ -0,0 +1,148 @@
+<?php
+/**
+ *
+ * This file is part of the phpBB Forum Software package.
+ *
+ * @copyright (c) phpBB Limited <https://www.phpbb.com>
+ * @license       GNU General Public License, version 2 (GPL-2.0)
+ *
+ * For full copyright and license information, please see
+ * the docs/CREDITS.txt file.
+ *
+ */
+
+namespace phpbb\mention\source;
+
+abstract class base_group implements source_interface
+{
+	/** @var \phpbb\db\driver\driver_interface */
+	protected $db;
+
+	/** @var \phpbb\group\helper */
+	protected $helper;
+
+	/** @var \phpbb\user */
+	protected $user;
+
+	/** @var \phpbb\auth\auth */
+	protected $auth;
+
+	/** @var string */
+	protected $phpbb_root_path;
+
+	/** @var string */
+	protected $php_ext;
+
+	/**
+	 * Constructor
+	 */
+	public function __construct(\phpbb\db\driver\driver_interface $db, \phpbb\group\helper $helper, \phpbb\user $user, \phpbb\auth\auth $auth, $phpbb_root_path, $phpEx)
+	{
+		$this->db = $db;
+		$this->helper = $helper;
+		$this->user = $user;
+		$this->auth = $auth;
+		$this->phpbb_root_path = $phpbb_root_path;
+		$this->php_ext = $phpEx;
+
+		if (!function_exists('phpbb_get_user_rank'))
+		{
+			include($this->phpbb_root_path . 'includes/functions_display.' . $this->php_ext);
+		}
+	}
+
+	/**
+	 * Returns data for all board groups
+	 *
+	 * @return array Array of groups' data
+	 */
+	protected function get_groups()
+	{
+		static $groups = null;
+
+		if (is_null($groups))
+		{
+			$query = $this->db->sql_build_query('SELECT', [
+				'SELECT' => 'g.*, ug.user_id as ug_user_id',
+				'FROM'   => [
+					GROUPS_TABLE => 'g',
+				],
+				'LEFT_JOIN'	=> array(
+					array(
+						'FROM'	=> array(USER_GROUP_TABLE => 'ug'),
+						'ON'	=> 'ug.group_id = g.group_id AND ug.user_pending = 0 AND ug.user_id = ' . (int) $this->user->data['user_id'],
+					),
+				),
+			]);
+			$result = $this->db->sql_query($query);
+
+			$groups = [];
+			while ($row = $this->db->sql_fetchrow($result))
+			{
+				if ($row['group_type'] == GROUP_SPECIAL && !in_array($row['group_name'], ['ADMINISTRATORS', 'GLOBAL_MODERATORS']) || $row['group_type'] == GROUP_HIDDEN && !$this->auth->acl_gets('a_group', 'a_groupadd', 'a_groupdel') && $row['ug_user_id'] != $this->user->data['user_id'])
+				{
+					// Skip the group that we should not be able to mention.
+					continue;
+				}
+
+				$group_name = $this->helper->get_name($row['group_name']);
+				$groups['names'][$row['group_id']] = $group_name;
+				$groups[$row['group_id']] = $row;
+				$groups[$row['group_id']]['group_name'] = $group_name;
+			}
+
+			$this->db->sql_freeresult($result);
+		}
+		return $groups;
+	}
+
+	/**
+	 * Builds a query for getting group IDs based on user input
+	 *
+	 * @param string $keyword  Search string
+	 * @param int    $topic_id Current topic ID
+	 * @return string Query ready for execution
+	 */
+	abstract protected function query($keyword, $topic_id);
+
+	/**
+	 * {@inheritdoc}
+	 */
+	public function get($keyword, $topic_id)
+	{
+		// Grab all group IDs
+		$result = $this->db->sql_query($this->query($keyword, $topic_id));
+
+		$group_ids = [];
+		while ($row = $this->db->sql_fetchrow($result))
+		{
+			$group_ids[] = $row['group_id'];
+		}
+
+		$this->db->sql_freeresult($result);
+
+		// Grab group data
+		$groups = $this->get_groups();
+
+		$matches = preg_grep('/^' . $keyword . '.*/i', $groups['names']);
+		$group_ids = array_intersect($group_ids, array_flip($matches));
+
+		$names = [];
+		foreach ($group_ids as $group_id)
+		{
+			$group_rank = phpbb_get_user_rank($groups[$group_id], false);
+			$names['g' . $group_id] = [
+				'name'		=> $groups[$group_id]['group_name'],
+				'param'		=> 'group_id',
+				'id'		=> $group_id,
+				'avatar'	=> [
+					'type'	=> 'group',
+					'src'	=> phpbb_get_group_avatar($groups[$group_id]),
+				],
+				'rank'		=> $group_rank['title'],
+			];
+		}
+
+		return $names;
+	}
+}
diff --git a/phpBB/phpbb/mention/source/base_user.php b/phpBB/phpbb/mention/source/base_user.php
new file mode 100644
index 0000000000..d23d3db02e
--- /dev/null
+++ b/phpBB/phpbb/mention/source/base_user.php
@@ -0,0 +1,83 @@
+<?php
+/**
+ *
+ * This file is part of the phpBB Forum Software package.
+ *
+ * @copyright (c) phpBB Limited <https://www.phpbb.com>
+ * @license       GNU General Public License, version 2 (GPL-2.0)
+ *
+ * For full copyright and license information, please see
+ * the docs/CREDITS.txt file.
+ *
+ */
+
+namespace phpbb\mention\source;
+
+abstract class base_user implements source_interface
+{
+	/** @var \phpbb\db\driver\driver_interface */
+	protected $db;
+
+	/** @var \phpbb\user_loader */
+	protected $user_loader;
+
+	/** @var string */
+	protected $phpbb_root_path;
+
+	/** @var string */
+	protected $php_ext;
+
+	/**
+	 * Constructor
+	 */
+	public function __construct(\phpbb\db\driver\driver_interface $db, \phpbb\user_loader $user_loader, $phpbb_root_path, $phpEx)
+	{
+		$this->db = $db;
+		$this->user_loader = $user_loader;
+		$this->phpbb_root_path = $phpbb_root_path;
+		$this->php_ext = $phpEx;
+
+		if (!function_exists('phpbb_get_user_rank'))
+		{
+			include($this->phpbb_root_path . 'includes/functions_display.' . $this->php_ext);
+		}
+	}
+
+	/**
+	 * Builds a query based on user input
+	 *
+	 * @param string $keyword  Search string
+	 * @param int    $topic_id Current topic ID
+	 * @return string Query ready for execution
+	 */
+	abstract protected function query($keyword, $topic_id);
+
+	/**
+	 * {@inheritdoc}
+	 */
+	public function get($keyword, $topic_id)
+	{
+		$keyword = utf8_clean_string($keyword);
+		$result = $this->db->sql_query_limit($this->query($keyword, $topic_id), 5);
+
+		$names = [];
+		while ($row = $this->db->sql_fetchrow($result))
+		{
+			$user_rank = $this->user_loader->get_rank($row['user_id'], true);
+			$names['u' . $row['user_id']] = [
+				'name'		=> $row['username'],
+				'param'		=> 'user_id',
+				'id'		=> $row['user_id'],
+				'avatar'	=> [
+					'type'	=> 'user',
+					'src'	=> $this->user_loader->get_avatar($row['user_id'], true),
+				],
+				'rank'		=> (isset($user_rank['rank_title'])) ? $user_rank['rank_title'] : '',
+			];
+		}
+
+		$this->db->sql_freeresult($result);
+
+		return $names;
+	}
+}
diff --git a/phpBB/phpbb/mention/source/friend.php b/phpBB/phpbb/mention/source/friend.php
index b3c6a1898b..3c946dcd73 100644
--- a/phpBB/phpbb/mention/source/friend.php
+++ b/phpBB/phpbb/mention/source/friend.php
@@ -13,7 +13,7 @@
 
 namespace phpbb\mention\source;
 
-class friend extends user
+class friend extends base_user
 {
 	/** @var  \phpbb\user */
 	protected $user;
diff --git a/phpBB/phpbb/mention/source/group.php b/phpBB/phpbb/mention/source/group.php
index 92619ee772..d063d64324 100644
--- a/phpBB/phpbb/mention/source/group.php
+++ b/phpBB/phpbb/mention/source/group.php
@@ -13,116 +13,19 @@
 
 namespace phpbb\mention\source;
 
-abstract class group implements source_interface
+class group extends base_group
 {
-	/** @var \phpbb\db\driver\driver_interface */
-	protected $db;
-
-	/** @var \phpbb\group\helper */
-	protected $helper;
-
-	/** @var string */
-	protected $phpbb_root_path;
-
-	/** @var string */
-	protected $php_ext;
-
-	/**
-	 * Constructor
-	 */
-	public function __construct(\phpbb\db\driver\driver_interface $db, \phpbb\group\helper $helper, $phpbb_root_path, $phpEx)
-	{
-		$this->db = $db;
-		$this->helper = $helper;
-		$this->phpbb_root_path = $phpbb_root_path;
-		$this->php_ext = $phpEx;
-
-		if (!function_exists('phpbb_get_user_rank'))
-		{
-			include($this->phpbb_root_path . 'includes/functions_display.' . $this->php_ext);
-		}
-	}
-
-	/**
-	 * Returns data for all board groups
-	 *
-	 * @return array Array of groups' data
-	 */
-	protected function get_groups()
-	{
-		static $groups = null;
-
-		if (is_null($groups))
-		{
-			$query = $this->db->sql_build_query('SELECT', [
-				'SELECT' => 'g.*',
-				'FROM'   => [
-					GROUPS_TABLE => 'g',
-				],
-			]);
-			$result = $this->db->sql_query($query);
-
-			$groups = [];
-			while ($row = $this->db->sql_fetchrow($result))
-			{
-				$group_name = $this->helper->get_name($row['group_name']);
-				$groups['names'][$row['group_id']] = $group_name;
-				$groups[$row['group_id']] = $row;
-				$groups[$row['group_id']]['group_name'] = $group_name;
-			}
-
-			$this->db->sql_freeresult($result);
-		}
-		return $groups;
-	}
-
-	/**
-	 * Builds a query for getting group IDs based on user input
-	 *
-	 * @param string $keyword  Search string
-	 * @param int    $topic_id Current topic ID
-	 * @return string Query ready for execution
-	 */
-	abstract protected function query($keyword, $topic_id);
-
 	/**
 	 * {@inheritdoc}
 	 */
-	public function get($keyword, $topic_id)
+	protected function query($keyword, $topic_id)
 	{
-		// Grab all group IDs
-		$result = $this->db->sql_query($this->query($keyword, $topic_id));
-
-		$group_ids = [];
-		while ($row = $this->db->sql_fetchrow($result))
-		{
-			$group_ids[] = $row['group_id'];
-		}
-
-		$this->db->sql_freeresult($result);
-
-		// Grab group data
-		$groups = $this->get_groups();
-
-		$matches = preg_grep('/^' . $keyword . '.*/i', $groups['names']);
-		$group_ids = array_intersect($group_ids, array_flip($matches));
-
-		$names = [];
-		foreach ($group_ids as $group_id)
-		{
-			$group_rank = phpbb_get_user_rank($groups[$group_id], false);
-			$names['g' . $group_id] = [
-				'name'		=> $groups[$group_id]['group_name'],
-				'param'		=> 'group_id',
-				'id'		=> $group_id,
-				'avatar'	=> [
-					'type'	=> 'group',
-					'src'	=> phpbb_get_group_avatar($groups[$group_id]),
-				],
-				'rank'		=> $group_rank['title'],
-			];
-		}
-
-		return $names;
+		$query = $this->db->sql_build_query('SELECT', [
+			'SELECT'    => 'g.group_id',
+			'FROM'      => [
+				GROUPS_TABLE => 'g',
+			],
+		]);
+		return $query;
 	}
 }
diff --git a/phpBB/phpbb/mention/source/member.php b/phpBB/phpbb/mention/source/member.php
deleted file mode 100644
index bc1c5960ee..0000000000
--- a/phpBB/phpbb/mention/source/member.php
+++ /dev/null
@@ -1,35 +0,0 @@
-<?php
-/**
- *
- * This file is part of the phpBB Forum Software package.
- *
- * @copyright (c) phpBB Limited <https://www.phpbb.com>
- * @license       GNU General Public License, version 2 (GPL-2.0)
- *
- * For full copyright and license information, please see
- * the docs/CREDITS.txt file.
- *
- */
-
-namespace phpbb\mention\source;
-
-class member extends user
-{
-	/**
-	 * {@inheritdoc}
-	 */
-	protected function query($keyword, $topic_id)
-	{
-		$query = $this->db->sql_build_query('SELECT', [
-			'SELECT'    => 'u.username, u.user_id',
-			'FROM'      => [
-				USERS_TABLE => 'u',
-			],
-			'WHERE'     => 'u.user_id <> ' . ANONYMOUS . '
-				AND ' . $this->db->sql_in_set('u.user_type', [USER_NORMAL, USER_FOUNDER]) . '
-				AND u.username_clean ' . $this->db->sql_like_expression($keyword . $this->db->get_any_char()),
-			'ORDER_BY'  => 'u.user_lastvisit DESC'
-		]);
-		return $query;
-	}
-}
diff --git a/phpBB/phpbb/mention/source/team.php b/phpBB/phpbb/mention/source/team.php
index dce5630944..187f0fb691 100644
--- a/phpBB/phpbb/mention/source/team.php
+++ b/phpBB/phpbb/mention/source/team.php
@@ -13,7 +13,7 @@
 
 namespace phpbb\mention\source;
 
-class team extends user
+class team extends base_user
 {
 	/**
 	 * {@inheritdoc}
diff --git a/phpBB/phpbb/mention/source/topic.php b/phpBB/phpbb/mention/source/topic.php
index 1d72df711c..f8a5123c56 100644
--- a/phpBB/phpbb/mention/source/topic.php
+++ b/phpBB/phpbb/mention/source/topic.php
@@ -13,7 +13,7 @@
 
 namespace phpbb\mention\source;
 
-class topic extends user
+class topic extends base_user
 {
 	/**
 	 * {@inheritdoc}
diff --git a/phpBB/phpbb/mention/source/user.php b/phpBB/phpbb/mention/source/user.php
index 466bda36db..10f065df0d 100644
--- a/phpBB/phpbb/mention/source/user.php
+++ b/phpBB/phpbb/mention/source/user.php
@@ -13,71 +13,23 @@
 
 namespace phpbb\mention\source;
 
-abstract class user implements source_interface
+class user extends base_user
 {
-	/** @var \phpbb\db\driver\driver_interface */
-	protected $db;
-
-	/** @var \phpbb\user_loader */
-	protected $user_loader;
-
-	/** @var string */
-	protected $phpbb_root_path;
-
-	/** @var string */
-	protected $php_ext;
-
-	/**
-	 * Constructor
-	 */
-	public function __construct(\phpbb\db\driver\driver_interface $db, \phpbb\user_loader $user_loader, $phpbb_root_path, $phpEx)
-	{
-		$this->db = $db;
-		$this->user_loader = $user_loader;
-		$this->phpbb_root_path = $phpbb_root_path;
-		$this->php_ext = $phpEx;
-
-		if (!function_exists('phpbb_get_user_rank'))
-		{
-			include($this->phpbb_root_path . 'includes/functions_display.' . $this->php_ext);
-		}
-	}
-
-	/**
-	 * Builds a query based on user input
-	 *
-	 * @param string $keyword  Search string
-	 * @param int    $topic_id Current topic ID
-	 * @return string Query ready for execution
-	 */
-	abstract protected function query($keyword, $topic_id);
-
 	/**
 	 * {@inheritdoc}
 	 */
-	public function get($keyword, $topic_id)
+	protected function query($keyword, $topic_id)
 	{
-		$keyword = utf8_clean_string($keyword);
-		$result = $this->db->sql_query_limit($this->query($keyword, $topic_id), 5);
-
-		$names = [];
-		while ($row = $this->db->sql_fetchrow($result))
-		{
-			$user_rank = $this->user_loader->get_rank($row['user_id'], true);
-			$names['u' . $row['user_id']] = [
-				'name'		=> $row['username'],
-				'param'		=> 'user_id',
-				'id'		=> $row['user_id'],
-				'avatar'	=> [
-					'type'	=> 'user',
-					'src'	=> $this->user_loader->get_avatar($row['user_id'], true),
-				],
-				'rank'		=> (isset($user_rank['rank_title'])) ? $user_rank['rank_title'] : '',
-			];
-		}
-
-		$this->db->sql_freeresult($result);
-
-		return $names;
+		$query = $this->db->sql_build_query('SELECT', [
+			'SELECT'    => 'u.username, u.user_id',
+			'FROM'      => [
+				USERS_TABLE => 'u',
+			],
+			'WHERE'     => 'u.user_id <> ' . ANONYMOUS . '
+				AND ' . $this->db->sql_in_set('u.user_type', [USER_NORMAL, USER_FOUNDER]) . '
+				AND u.username_clean ' . $this->db->sql_like_expression($keyword . $this->db->get_any_char()),
+			'ORDER_BY'  => 'u.user_lastvisit DESC'
+		]);
+		return $query;
 	}
 }
diff --git a/phpBB/phpbb/mention/source/usergroup.php b/phpBB/phpbb/mention/source/usergroup.php
index 6d965961be..c3b95ffb49 100644
--- a/phpBB/phpbb/mention/source/usergroup.php
+++ b/phpBB/phpbb/mention/source/usergroup.php
@@ -13,21 +13,8 @@
 
 namespace phpbb\mention\source;
 
-class usergroup extends group
+class usergroup extends base_group
 {
-	/** @var  \phpbb\user */
-	protected $user;
-
-	/**
-	 * Constructor
-	 */
-	public function __construct(\phpbb\db\driver\driver_interface $db, \phpbb\group\helper $helper, \phpbb\user $user, $phpbb_root_path, $phpEx)
-	{
-		$this->user = $user;
-
-		parent::__construct($db, $helper, $phpbb_root_path, $phpEx);
-	}
-
 	/**
 	 * {@inheritdoc}
 	 */