diff --git a/calendar/externallib.php b/calendar/externallib.php
index 0aeb9a4e8a8..e644e399710 100644
--- a/calendar/externallib.php
+++ b/calendar/externallib.php
@@ -356,6 +356,8 @@ class core_calendar_external extends external_api {
                             'description' => new external_value(PARAM_RAW, 'Description', VALUE_OPTIONAL, null, NULL_ALLOWED),
                             'format' => new external_format_value('description'),
                             'courseid' => new external_value(PARAM_INT, 'course id'),
+                            'categoryid' => new external_value(PARAM_INT, 'Category id (only for category events).',
+                                VALUE_OPTIONAL),
                             'groupid' => new external_value(PARAM_INT, 'group id'),
                             'userid' => new external_value(PARAM_INT, 'user id'),
                             'repeatid' => new external_value(PARAM_INT, 'repeat id'),
diff --git a/calendar/tests/externallib_test.php b/calendar/tests/externallib_test.php
index 42e3b0ecf08..9fcf147e005 100644
--- a/calendar/tests/externallib_test.php
+++ b/calendar/tests/externallib_test.php
@@ -506,6 +506,7 @@ class core_calendar_externallib_testcase extends externallib_advanced_testcase {
         // Should be just one, since there's just one category event of the course I am enrolled (course3 - cat2b).
         $this->assertEquals(1, count($events['events']));
         $this->assertEquals($catevent2->id, $events['events'][0]['id']);
+        $this->assertEquals($category2->id, $events['events'][0]['categoryid']);
         $this->assertEquals(0, count($events['warnings']));
 
         // Now get category events but by course (there aren't course events in the course).
@@ -536,7 +537,9 @@ class core_calendar_externallib_testcase extends externallib_advanced_testcase {
         $this->assertEquals(2, count($events['events']));
         $this->assertEquals(0, count($events['warnings']));
         $this->assertEquals($catevent1->id, $events['events'][0]['id']);
+        $this->assertEquals($category->id, $events['events'][0]['categoryid']);
         $this->assertEquals($catevent2->id, $events['events'][1]['id']);
+        $this->assertEquals($category2->id, $events['events'][1]['categoryid']);
     }
 
     /**
diff --git a/calendar/upgrade.txt b/calendar/upgrade.txt
index b2973e53f0a..359ee3e796b 100644
--- a/calendar/upgrade.txt
+++ b/calendar/upgrade.txt
@@ -1,6 +1,9 @@
 This files describes API changes in /calendar/* ,
 information provided here is intended especially for developers.
 
+=== 3.5 ===
+* core_calendar_external::get_calendar_events now returns the categoryid for category events.
+
 === 3.4 ===
 * calendar_get_mini, and calendar_get_upcoming have been deprecated. Please update to use the new exporters and renderers.
 * added core_calendar_get_valid_event_timestart_range and core_calendar_event_timestart_updated callbacks for module events