diff --git a/backup/backup.php b/backup/backup.php
index 59b0d34d208..703e77b577b 100644
--- a/backup/backup.php
+++ b/backup/backup.php
@@ -117,7 +117,9 @@
     //Call the form, depending the step we are
     if (!$launch) {
         // if we're at the start, clear the cache of prefs
-        unset($SESSION->backupprefs[$course->id]);
+        if (isset($SESSION->backupprefs[$course->id])) {
+            unset($SESSION->backupprefs[$course->id]);
+        }
         include_once("backup_form.html");
     } else if ($launch == "check") {
         include_once("backup_check.html");