diff --git a/lib/external/classes/external_description.php b/lib/external/classes/external_description.php
new file mode 100644
index 00000000000..cc8c59750af
--- /dev/null
+++ b/lib/external/classes/external_description.php
@@ -0,0 +1,50 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+namespace core_external;
+
+/**
+ * Common ancestor of all parameter description classes
+ *
+ * @package    core_webservice
+ * @copyright  2009 Petr Skodak
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @since Moodle 2.0
+ */
+abstract class external_description {
+    /** @var string Description of element */
+    public $desc;
+
+    /** @var bool Element value required, null not allowed */
+    public $required;
+
+    /** @var mixed Default value */
+    public $default;
+
+    /**
+     * Contructor
+     *
+     * @param string $desc
+     * @param bool $required
+     * @param mixed $default
+     * @since Moodle 2.0
+     */
+    public function __construct($desc, $required, $default) {
+        $this->desc = $desc;
+        $this->required = $required;
+        $this->default = $default;
+    }
+}
diff --git a/lib/externallib.php b/lib/externallib.php
index f5b975446f9..7e79ece5eab 100644
--- a/lib/externallib.php
+++ b/lib/externallib.php
@@ -45,39 +45,7 @@ class restricted_context_exception extends moodle_exception {
 }
 
 class_alias(\core_external\external_api::class, 'external_api');
-
-/**
- * Common ancestor of all parameter description classes
- *
- * @package    core_webservice
- * @copyright  2009 Petr Skodak
- * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
- * @since Moodle 2.0
- */
-abstract class external_description {
-    /** @var string Description of element */
-    public $desc;
-
-    /** @var bool Element value required, null not allowed */
-    public $required;
-
-    /** @var mixed Default value */
-    public $default;
-
-    /**
-     * Contructor
-     *
-     * @param string $desc
-     * @param bool $required
-     * @param mixed $default
-     * @since Moodle 2.0
-     */
-    public function __construct($desc, $required, $default) {
-        $this->desc = $desc;
-        $this->required = $required;
-        $this->default = $default;
-    }
-}
+class_alias(\core_external\external_description::class, 'external_description');
 
 /**
  * Scalar value description class