diff --git a/phpBB/includes/captcha/captcha_factory.php b/phpBB/includes/captcha/captcha_factory.php
index 1ed8e119b5..fac45087e3 100644
--- a/phpBB/includes/captcha/captcha_factory.php
+++ b/phpBB/includes/captcha/captcha_factory.php
@@ -50,7 +50,8 @@ class phpbb_captcha_factory
 		{
 			include($phpbb_root_path . "includes/captcha/plugins/{$name}_plugin." . $phpEx);
 		}
-		call_user_func(array($name, 'garbage_collect'), 0);
+		$captcha = self::get_instance($name);
+		$captcha->garbage_collect(0);
 	}
 
 	/**
diff --git a/phpBB/phpbb/session.php b/phpBB/phpbb/session.php
index e0585b1523..dc33786666 100644
--- a/phpBB/phpbb/session.php
+++ b/phpBB/phpbb/session.php
@@ -1022,7 +1022,8 @@ class phpbb_session
 			{
 				include($phpbb_root_path . "includes/captcha/captcha_factory." . $phpEx);
 			}
-			phpbb_captcha_factory::garbage_collect($config['captcha_plugin']);
+			$captcha_factory = new phpbb_captcha_factory();
+			$captcha_factory->garbage_collect($config['captcha_plugin']);
 
 			$sql = 'DELETE FROM ' . LOGIN_ATTEMPT_TABLE . '
 				WHERE attempt_time < ' . (time() - (int) $config['ip_login_limit_time']);