diff --git a/backup/moodle2/restore_attendance_activity_task.class.php b/backup/moodle2/restore_attendance_activity_task.class.php
index d30493d..ec9e199 100644
--- a/backup/moodle2/restore_attendance_activity_task.class.php
+++ b/backup/moodle2/restore_attendance_activity_task.class.php
@@ -110,4 +110,28 @@ class restore_attendance_activity_task extends restore_activity_task {
 
         return $rules;
     }
+
+    /**
+     * After restore - clean up any incorrect calendar items that have been restored.
+     * @throws dml_exception
+     */
+    public function after_restore() {
+        global $DB;
+        $attendanceid = $this->get_activityid();
+        $courseid = $this->get_courseid();
+        if (empty($courseid) || empty($attendanceid)) {
+            return;
+        }
+        if (empty(get_config('attendance', 'enablecalendar'))) {
+            // Attendance isn't using Calendar - delete anything that was created.
+            $DB->delete_records('event', ['modulename' => 'attendance', 'instance' => $attendanceid, 'courseid' => $courseid]);
+        } else {
+            // Clean up any orphaned events.
+            $sql = "modulename = 'attendance' AND courseid = :courseid AND id NOT IN (SELECT caleventid
+                                                                                        FROM {attendance_sessions}
+                                                                                       WHERE attendanceid = :attendanceid)";
+            $params = ['courseid' => $courseid, 'attendanceid' => $attendanceid];
+            $DB->delete_records_select('event', $sql, $params);
+        }
+    }
 }
diff --git a/backup/moodle2/restore_attendance_stepslib.php b/backup/moodle2/restore_attendance_stepslib.php
index ae7cad8..efdfec1 100644
--- a/backup/moodle2/restore_attendance_stepslib.php
+++ b/backup/moodle2/restore_attendance_stepslib.php
@@ -178,7 +178,7 @@ class restore_attendance_activity_structure_step extends restore_activity_struct
     }
 
     /**
-     * Once the database tables have been fully restored, restore the files
+     * Once the database tables have been fully restored, restore the files and clean up any calendar stuff.
      * @return void
      */
     protected function after_execute() {
diff --git a/db/upgrade.php b/db/upgrade.php
index f86843c..2ea545d 100755
--- a/db/upgrade.php
+++ b/db/upgrade.php
@@ -640,5 +640,16 @@ function xmldb_attendance_upgrade($oldversion=0) {
         upgrade_mod_savepoint(true, 2020072900, 'attendance');
     }
 
+    if ($oldversion < 2021050700) {
+        // Restore process sometimes creates orphan attendance calendar events - clean them up.
+        $sql = "modulename = 'attendance' AND id NOT IN (SELECT caleventid
+                                                           FROM {attendance_sessions})";
+        $DB->delete_records_select('event', $sql);
+
+        // Attendance savepoint reached.
+        upgrade_mod_savepoint(true, 2021050700, 'attendance');
+    }
+
+
     return $result;
 }
diff --git a/resetcalendar.php b/resetcalendar.php
index 129b5dd..6b0ac3b 100644
--- a/resetcalendar.php
+++ b/resetcalendar.php
@@ -70,10 +70,8 @@ if (get_config('attendance', 'enablecalendar')) {
     }
 } else {
     if ($action == 'delete' && confirm_sesskey()) {
-        $caleventids = $DB->get_records_select_menu('attendance_sessions', 'caleventid > 0', array(),
-                                                     '', 'caleventid, caleventid as id2');
-        $DB->delete_records_list('event', 'id', $caleventids);
-        $DB->execute("UPDATE {attendance_sessions} set caleventid = 0");
+        // Attendance isn't using Calendar - delete anything that was created.
+        $DB->delete_records('event', ['modulename' => 'attendance', 'eventtype' => 'attendance']);
         echo $OUTPUT->notification(get_string('eventsdeleted', 'mod_attendance'), 'notifysuccess');
     } else {
         // Check to see if there are any events that need to be deleted.
diff --git a/version.php b/version.php
index ed84199..02e6f12 100755
--- a/version.php
+++ b/version.php
@@ -23,7 +23,7 @@
  */
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version  = 2021011500;
+$plugin->version  = 2021050700;
 $plugin->requires = 2019072500; // Requires 3.8.
 $plugin->release = '3.9.1';
 $plugin->maturity  = MATURITY_STABLE;