diff --git a/mod/assign/classes/event/submission_unlocked.php b/mod/assign/classes/event/submission_unlocked.php
new file mode 100644
index 00000000000..e17841cef61
--- /dev/null
+++ b/mod/assign/classes/event/submission_unlocked.php
@@ -0,0 +1,113 @@
+<?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/>.
+
+/**
+ * mod_assign submission unlocked event.
+ *
+ * @package    mod_assign
+ * @copyright  2013 Frédéric Massart
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_assign\event;
+
+defined('MOODLE_INTERNAL') || die();
+
+/**
+ * mod_assign submission unlocked event class.
+ *
+ * @package    mod_assign
+ * @copyright  2013 Frédéric Massart
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class submission_unlocked extends \core\event\base {
+
+    /**
+     * Legacy log data.
+     *
+     * @var array
+     */
+    protected $legacylogdata;
+
+    /**
+     * Returns description of what happened.
+     *
+     * @return string
+     */
+    public function get_description() {
+        return "User {$this->userid} unlocked the submission for user {$this->relateduserid}.";
+    }
+
+    /**
+     * Return legacy data for add_to_log().
+     *
+     * @return array
+     */
+    public function get_legacy_logdata() {
+        return $this->legacylogdata;
+    }
+
+    /**
+     * Return localised event name.
+     *
+     * @return \lang_string
+     */
+    public static function get_name() {
+        return new \lang_string('event_submission_unlocked', 'mod_assign');
+    }
+
+    /**
+     * Get URL related to the action
+     *
+     * @return \moodle_url
+     */
+    public function get_url() {
+        return new \moodle_url('/mod/assign/view.php', array('id' => $this->context->instanceid));
+    }
+
+    /**
+     * Init method.
+     *
+     * @return void
+     */
+    protected function init() {
+        $this->data['crud'] = 'u';
+        $this->data['level'] = 50;          // TODO MDL-37658.
+        $this->data['objecttable'] = 'assign';
+    }
+
+    /**
+     * Sets the legacy event log data.
+     *
+     * @param stdClass $legacylogdata legacy log data.
+     * @return void
+     */
+    public function set_legacy_logdata($legacylogdata) {
+        $this->legacylogdata = $legacylogdata;
+    }
+
+    /**
+     * Custom validation.
+     *
+     * @throws coding_exception
+     * @return void
+     */
+    protected function validate_data() {
+        if (!isset($this->relateduserid)) {
+            throw new coding_exception('relateduserid is a mandatory property.');
+        }
+    }
+}
diff --git a/mod/assign/lang/en/assign.php b/mod/assign/lang/en/assign.php
index 26e0c9a1439..f590ab98541 100644
--- a/mod/assign/lang/en/assign.php
+++ b/mod/assign/lang/en/assign.php
@@ -149,6 +149,7 @@ $string['event_statement_accepted'] = 'The user has accepted the statement of th
 $string['event_submission_duplicated'] = 'The user duplicated his submission.';
 $string['event_submission_locked'] = 'The submissions have been locked for a user.';
 $string['event_submission_status_updated'] = 'The status of the submission has been updated.';
+$string['event_submission_unlocked'] = 'The submissions have been unlocked for a user.';
 $string['event_submission_updated'] = 'The user has saved a submission.';
 $string['event_workflow_state_updated'] = 'The state of the workflow has been updated.';
 $string['extensionduedate'] = 'Extension due date';
diff --git a/mod/assign/locallib.php b/mod/assign/locallib.php
index 99201b479a8..4355b0f3ae7 100644
--- a/mod/assign/locallib.php
+++ b/mod/assign/locallib.php
@@ -5886,7 +5886,15 @@ class assign {
         $logmessage = get_string('unlocksubmissionforstudent',
                                  'assign',
                                  array('id'=>$user->id, 'fullname'=>fullname($user)));
-        $this->add_to_log('unlock submission', $logmessage);
+        $addtolog = $this->add_to_log('unlock submission', $logmessage, '', true);
+        $params = array(
+            'context' => $this->context,
+            'objectid' => $flags->assignment,
+            'relateduserid' => $user->id
+        );
+        $event = \mod_assign\event\submission_unlocked::create($params);
+        $event->set_legacy_logdata($addtolog);
+        $event->trigger();
     }
 
     /**
diff --git a/mod/assign/tests/base_test.php b/mod/assign/tests/base_test.php
index ff01dbdb85e..17db4f23a0d 100644
--- a/mod/assign/tests/base_test.php
+++ b/mod/assign/tests/base_test.php
@@ -263,6 +263,10 @@ class testable_assign extends assign {
         return parent::process_lock($userid);
     }
 
+    public function testable_process_unlock($userid = 0) {
+        return parent::process_unlock($userid);
+    }
+
     public function testable_process_copy_previous_attempt(&$notices) {
         return parent::process_copy_previous_attempt($notices);
     }
diff --git a/mod/assign/tests/locallib_test.php b/mod/assign/tests/locallib_test.php
index 587e64bcf2a..494a271f3c2 100644
--- a/mod/assign/tests/locallib_test.php
+++ b/mod/assign/tests/locallib_test.php
@@ -1177,5 +1177,38 @@ class mod_assign_locallib_testcase extends mod_assign_base_testcase {
         $sink->close();
     }
 
+    public function test_submission_unlocked_event() {
+        $this->editingteachers[0]->ignoresesskey = true;
+        $this->setUser($this->editingteachers[0]);
+
+        $assign = $this->create_instance();
+        $sink = $this->redirectEvents();
+
+        $assign->testable_process_unlock($this->students[0]->id);
+
+        $events = $sink->get_events();
+        $this->assertCount(1, $events);
+        $event = reset($events);
+        $this->assertInstanceOf('\mod_assign\event\submission_unlocked', $event);
+        $this->assertEquals($assign->get_context(), $event->get_context());
+        $this->assertEquals($assign->get_instance()->id, $event->objectid);
+        $this->assertEquals($this->students[0]->id, $event->relateduserid);
+        $expected = array(
+            $assign->get_course()->id,
+            'assign',
+            'unlock submission',
+            'view.php?id=' . $assign->get_course_module()->id,
+            get_string('unlocksubmissionforstudent', 'assign', array('id' => $this->students[0]->id,
+                'fullname' => fullname($this->students[0]))),
+            $assign->get_course_module()->id,
+            $this->editingteachers[0]->id
+        );
+        $this->assertEventLegacyLogData($expected, $event);
+        $sink->close();
+
+        // Revert to defaults.
+        $this->editingteachers[0]->ignoresesskey = false;
+    }
+
 }