diff --git a/calendar/export_execute.php b/calendar/export_execute.php
index c604f22ed17a3..74755f2851fb1 100644
--- a/calendar/export_execute.php
+++ b/calendar/export_execute.php
@@ -215,10 +215,14 @@
         //dtend is better than duration, because it works in Microsoft Outlook and works better in Korganizer
         $ev->add_property('dtstart', Bennu::timestamp_to_datetime($event->timestart)); // when event starts.
         $ev->add_property('dtend', Bennu::timestamp_to_datetime($event->timestart + $event->timeduration));
+    } else if ($event->timeduration == 0) {
+        // When no duration is present, the event is instantaneous event, ex - Due date of a module.
+        // Moodle doesn't support all day events yet. See MDL-56227.
+        $ev->add_property('dtstart', Bennu::timestamp_to_datetime($event->timestart));
+        $ev->add_property('dtend', Bennu::timestamp_to_datetime($event->timestart));
     } else {
-        // When no duration is present, ie an all day event, VALUE should be date instead of time and dtend = dtstart + 1 day.
-        $ev->add_property('dtstart', Bennu::timestamp_to_date($event->timestart), array('value' => 'DATE')); // All day event.
-        $ev->add_property('dtend', Bennu::timestamp_to_date($event->timestart + DAYSECS), array('value' => 'DATE')); // All day event.
+        // This can be used to represent all day events in future.
+        throw new coding_exception("Negative duration is not supported yet.");
     }
     if ($event->courseid != 0) {
         $coursecontext = context_course::instance($event->courseid);
diff --git a/calendar/lib.php b/calendar/lib.php
index 55ad67fb8fec4..e2749eaba4951 100644
--- a/calendar/lib.php
+++ b/calendar/lib.php
@@ -2935,7 +2935,8 @@ function calendar_add_icalendar_event($event, $courseid, $subscriptionid, $timez
         // Check to see if the event started at Midnight on the imported calendar.
         date_default_timezone_set($timezone);
         if (date('H:i:s', $eventrecord->timestart) === "00:00:00") {
-            // This event should be an all day event.
+            // This event should be an all day event. This is not correct, we don't do anything differently for all day events.
+            // See MDL-56227.
             $eventrecord->timeduration = 0;
         }
         \core_date::set_default_server_timezone();
diff --git a/lib/bennu/iCalendar_components.php b/lib/bennu/iCalendar_components.php
index 9b9e313572c4e..83a1e5f573fb1 100644
--- a/lib/bennu/iCalendar_components.php
+++ b/lib/bennu/iCalendar_components.php
@@ -411,7 +411,7 @@ function invariant_holds() {
             // DTEND must be later than DTSTART
             // The standard is not clear on how to hande different value types though
             // TODO: handle this correctly even if the value types are different
-            if($this->properties['DTEND'][0]->value <= $this->properties['DTSTART'][0]->value) {
+            if($this->properties['DTEND'][0]->value < $this->properties['DTSTART'][0]->value) {
                 return false;
             }
 
diff --git a/lib/bennu/readme_moodle.txt b/lib/bennu/readme_moodle.txt
index e33a956898af6..845664cf3c1ef 100644
--- a/lib/bennu/readme_moodle.txt
+++ b/lib/bennu/readme_moodle.txt
@@ -8,3 +8,4 @@ modifications:
 5/ updated DTEND;TZID and DTSTAR;TZID values to support quotations (7 Nov 2014)
 6/ MDL-49032: fixed rfc2445_fold() to fix incorrect RFC2445_WSP definition (16 Sep 2015)
 7/ added timestamp_to_date function to support zero duration events (16 Sept 2015)
+8/ Updated \iCalendar_event::invariant_holds() to allow for same dtstart and dtend timestamps (13 July 2017)