diff --git a/phpBB/adm/index.php b/phpBB/adm/index.php
index 564a19ce64..8cd1967c75 100644
--- a/phpBB/adm/index.php
+++ b/phpBB/adm/index.php
@@ -50,7 +50,6 @@ $module_id		= request_var('i', '');
 $mode			= request_var('mode', '');
 
 // Set custom style for admin area
-$phpbb_style->set_ext_dir_prefix('adm/');
 $phpbb_style->set_custom_style('admin', $phpbb_admin_path . 'style', array(), '');
 $template->assign_var('T_ASSETS_PATH', $phpbb_root_path . 'assets');
 $template->assign_var('T_TEMPLATE_PATH', $phpbb_admin_path . 'style');
diff --git a/tests/functional/extension_module_test.php b/tests/functional/extension_module_test.php
new file mode 100644
index 0000000000..cf67675a28
--- /dev/null
+++ b/tests/functional/extension_module_test.php
@@ -0,0 +1,130 @@
+<?php
+/**
+*
+* @package testing
+* @copyright (c) 2013 phpBB Group
+* @license http://opensource.org/licenses/gpl-2.0.php GNU General Public License v2
+*
+*/
+
+require_once dirname(__FILE__) . '/../../phpBB/includes/db/db_tools.php';
+require_once dirname(__FILE__) . '/../../phpBB/includes/acp/acp_modules.php';
+
+/**
+* @group functional
+*/
+class phpbb_functional_extension_module_test extends phpbb_functional_test_case
+{
+	protected $phpbb_extension_manager;
+	static private $copied_files = array();
+	static private $helper;
+
+	/**
+	* This should only be called once before the tests are run.
+	* This is used to copy the fixtures to the phpBB install
+	*/
+	static public function setUpBeforeClass()
+	{
+		global $phpbb_root_path;
+		parent::setUpBeforeClass();
+
+		self::$helper = new phpbb_test_case_helpers(self);
+
+		self::$copied_files = array();
+
+		if (file_exists($phpbb_root_path . 'ext/'))
+		{
+			// First, move any extensions setup on the board to a temp directory
+			self::$copied_files = self::$helper->copy_dir($phpbb_root_path . 'ext/', $phpbb_root_path . 'store/temp_ext/');
+
+			// Then empty the ext/ directory on the board (for accurate test cases)
+			self::$helper->empty_dir($phpbb_root_path . 'ext/');
+		}
+
+		// Copy our ext/ files from the test case to the board
+		self::$copied_files = array_merge(self::$copied_files, self::$helper->copy_dir(dirname(__FILE__) . '/fixtures/ext/', $phpbb_root_path . 'ext/'));
+	}
+
+	/**
+	* This should only be called once after the tests are run.
+	* This is used to remove the fixtures from the phpBB install
+	*/
+	static public function tearDownAfterClass()
+	{
+		global $phpbb_root_path;
+
+		if (file_exists($phpbb_root_path . 'store/temp_ext/'))
+		{
+			// Copy back the board installed extensions from the temp directory
+			self::$helper->copy_dir($phpbb_root_path . 'store/temp_ext/', $phpbb_root_path . 'ext/');
+		}
+
+		// Remove all of the files we copied around (from board ext -> temp_ext, from test ext -> board ext)
+		self::$helper->remove_files(self::$copied_files);
+
+		if (file_exists($phpbb_root_path . 'store/temp_ext/'))
+		{
+			self::$helper->empty_dir($phpbb_root_path . 'store/temp_ext/');
+		}
+	}
+
+	public function setUp()
+	{
+		global $db;
+
+		parent::setUp();
+
+		$this->phpbb_extension_manager = $this->get_extension_manager();
+		$this->phpbb_extension_manager->enable('foo/bar');
+
+		$modules = new acp_modules();
+		$db = $this->get_db();
+
+		$sql = 'SELECT module_id
+			FROM ' . MODULES_TABLE . "
+			WHERE module_langname = 'acp'
+				AND module_class = 'ACP_CAT_DOT_MODS'";
+		$result = $db->sql_query($sql);
+		$module_id = (int) $db->sql_fetchfield('module_id');
+		$db->sql_freeresult($result);
+
+		$parent_data = array(
+			'module_basename'	=> '',
+			'module_enabled'	=> 1,
+			'module_display'	=> 1,
+			'parent_id'			=> $module_id,
+			'module_class'		=> 'acp',
+			'module_langname'	=> 'ACP_FOOBAR_TITLE',
+			'module_mode'		=> '',
+			'module_auth'		=> '',
+		);
+		$modules->update_module_data($parent_data, true);
+
+		$module_data = array(
+			'module_basename'	=> 'phpbb_ext_foo_bar_acp_main_module',
+			'module_enabled'	=> 1,
+			'module_display'	=> 1,
+			'parent_id'			=> $parent_data['module_id'],
+			'module_class'		=> 'acp',
+			'module_langname'	=> 'ACP_FOOBAR_TITLE',
+			'module_mode'		=> 'mode',
+			'module_auth'		=> '',
+		);
+		$modules->update_module_data($module_data, true);
+
+		$this->purge_cache();
+	}
+
+	/**
+	* Check a controller for extension foo/bar.
+	*/
+	public function test_foo_bar()
+	{
+		$this->login();
+		$this->admin_login();
+		$crawler = $this->request('GET', 'adm/index.php?i=phpbb_ext_foo_bar_acp_main_module&mode=mode&sid=' . $this->sid, array(), true);
+		$this->assert_response_success();
+		$this->assertContains("Bertie rulez!", $crawler->filter('#main')->text());
+		$this->phpbb_extension_manager->purge('foo/bar');
+	}
+}
diff --git a/tests/functional/fixtures/ext/foo/bar/acp/main_info.php b/tests/functional/fixtures/ext/foo/bar/acp/main_info.php
new file mode 100644
index 0000000000..21e38b09b5
--- /dev/null
+++ b/tests/functional/fixtures/ext/foo/bar/acp/main_info.php
@@ -0,0 +1,32 @@
+<?php
+
+/**
+*
+* @package testing
+* @copyright (c) 2013 phpBB Group
+* @license http://opensource.org/licenses/gpl-2.0.php GNU General Public License v2
+*
+*/
+
+/**
+* @ignore
+*/
+if (!defined('IN_PHPBB'))
+{
+	exit;
+}
+
+class phpbb_ext_foo_bar_acp_main_info
+{
+	function module()
+	{
+		return array(
+			'filename'	=> 'phpbb_ext_foo_bar_acp_main_module',
+			'title'		=> 'ACP_FOOBAR_TITLE',
+			'version'	=> '1.0.0',
+			'modes'		=> array(
+				'mode'		=> array('title' => 'ACP_FOOBAR_MODE', 'auth' => '', 'cat' => array('ACP_FOOBAR_TITLE')),
+			),
+		);
+	}
+}
diff --git a/tests/functional/fixtures/ext/foo/bar/acp/main_module.php b/tests/functional/fixtures/ext/foo/bar/acp/main_module.php
new file mode 100644
index 0000000000..c4ab69fb38
--- /dev/null
+++ b/tests/functional/fixtures/ext/foo/bar/acp/main_module.php
@@ -0,0 +1,28 @@
+<?php
+
+/**
+*
+* @package testing
+* @copyright (c) 2013 phpBB Group
+* @license http://opensource.org/licenses/gpl-2.0.php GNU General Public License v2
+*
+*/
+
+/**
+* @ignore
+*/
+if (!defined('IN_PHPBB'))
+{
+	exit;
+}
+
+class phpbb_ext_foo_bar_acp_main_module
+{
+	var $u_action;
+
+	function main($id, $mode)
+	{
+		$this->tpl_name = 'foobar';
+		$this->page_title = 'Bertie';
+	}
+}
diff --git a/tests/functional/fixtures/ext/foo/bar/adm/style/foobar.html b/tests/functional/fixtures/ext/foo/bar/adm/style/foobar.html
new file mode 100644
index 0000000000..3cb45c269c
--- /dev/null
+++ b/tests/functional/fixtures/ext/foo/bar/adm/style/foobar.html
@@ -0,0 +1,3 @@
+<!-- INCLUDE overall_header.html -->
+Bertie rulez!
+<!-- INCLUDE overall_footer.html -->