diff --git a/calendar/externallib.php b/calendar/externallib.php
index c2053fa9d48..da95699fab3 100644
--- a/calendar/externallib.php
+++ b/calendar/externallib.php
@@ -227,21 +227,21 @@ class core_calendar_external extends external_api {
             $params['options']['timeend'] = PHP_INT_MAX;
         }
 
+        // Event list does not check visibility and permissions, we'll check that later.
         $eventlist = calendar_get_events($params['options']['timestart'], $params['options']['timeend'], $funcparam['users'], $funcparam['groups'],
                 $funcparam['courses'], true, $params['options']['ignorehidden']);
+
         // WS expects arrays.
         $events = array();
-        foreach ($eventlist as $id => $event) {
-            $events[$id] = (array) $event;
-        }
 
         // We need to get events asked for eventids.
-        $eventsbyid = calendar_get_events_by_id($params['events']['eventids']);
-        foreach ($eventsbyid as $eventid => $eventobj) {
+        if ($eventsbyid = calendar_get_events_by_id($params['events']['eventids'])) {
+            $eventlist += $eventsbyid;
+        }
+
+        foreach ($eventlist as $eventid => $eventobj) {
             $event = (array) $eventobj;
-            if (isset($events[$eventid])) {
-                   continue;
-            }
+
             if ($hassystemcap) {
                 // User can see everything, no further check is needed.
                 $events[$eventid] = $event;
diff --git a/calendar/tests/externallib_test.php b/calendar/tests/externallib_test.php
index 8a5b444b823..7619b2a56bc 100644
--- a/calendar/tests/externallib_test.php
+++ b/calendar/tests/externallib_test.php
@@ -370,6 +370,30 @@ class core_calendar_externallib_testcase extends externallib_advanced_testcase {
         $events = external_api::clean_returnvalue(core_calendar_external::get_calendar_events_returns(), $events);
         $this->assertEquals(1, count($events['events']));
         $this->assertEquals(0, count($events['warnings']));
+
+        // Now, create an activity event.
+        $this->setAdminUser();
+        $nexttime = time() + DAYSECS;
+        $assign = $this->getDataGenerator()->create_module('assign', array('course' => $course->id, 'duedate' => $nexttime));
+
+        $this->setUser($user);
+        $paramevents = array ('courseids' => array($course->id));
+        $options = array ('siteevents' => true, 'userevents' => true, 'timeend' => time() + WEEKSECS);
+        $events = core_calendar_external::get_calendar_events($paramevents, $options);
+        $events = external_api::clean_returnvalue(core_calendar_external::get_calendar_events_returns(), $events);
+
+        $this->assertCount(5, $events['events']);
+
+        // Hide the assignment.
+        set_coursemodule_visible($assign->cmid, 0);
+        // Empty all the caches that may be affected  by this change.
+        accesslib_clear_all_caches_for_unit_testing();
+        course_modinfo::clear_instance_cache();
+
+        $events = core_calendar_external::get_calendar_events($paramevents, $options);
+        $events = external_api::clean_returnvalue(core_calendar_external::get_calendar_events_returns(), $events);
+        // Expect one less.
+        $this->assertCount(4, $events['events']);
     }
 
     /**