diff --git a/grade/export/lib.php b/grade/export/lib.php
index 32f2e27b44d..b71a7b30c09 100644
--- a/grade/export/lib.php
+++ b/grade/export/lib.php
@@ -230,7 +230,7 @@ abstract class grade_export {
             }
             $user = $userdata->user;
             if ($require_user_idnumber and empty($user->idnumber)) {
-                // some exports require user idnumber
+                // some exports require user idnumber so we can match up students when importing the data
                 continue;
             }
 
diff --git a/grade/export/xml/grade_export_xml.php b/grade/export/xml/grade_export_xml.php
index 1f65df45e9a..a978b0dbe20 100644
--- a/grade/export/xml/grade_export_xml.php
+++ b/grade/export/xml/grade_export_xml.php
@@ -58,7 +58,7 @@ class grade_export_xml extends grade_export {
             $user = $userdata->user;
 
             if (empty($user->idnumber)) {
-                //id number must exist
+                //id number must exist otherwise we cant match up students when importing
                 continue;
             }
 
diff --git a/grade/export/xml/index.php b/grade/export/xml/index.php
index cef6e6f496c..bc4d9251375 100644
--- a/grade/export/xml/index.php
+++ b/grade/export/xml/index.php
@@ -39,6 +39,7 @@ if (!empty($CFG->gradepublishing)) {
     $CFG->gradepublishing = has_capability('gradeexport/xml:publish', $context);
 }
 
+//'idnumberrequired'=>true excludes grade items that dont have an ID to use during import
 $mform = new grade_export_form(null, array('idnumberrequired'=>true, 'publishing'=>true, 'updategradesonly'=>true));
 
 $groupmode    = groups_get_course_groupmode($course);   // Groups are being used
@@ -56,7 +57,10 @@ if ($data = $mform->get_data()) {
     // print the grades on screen for feedbacks
     $export->process_form($data);
     $export->print_continue();
-    $export->display_preview(true);
+
+    $export->display_preview(true); //true == skip users without idnumber as they cannot be identified when importing
+    echo $OUTPUT->container(get_string('useridnumberwarning','gradeexport_xml'), 'useridnumberwarning mdl-align');
+
     echo $OUTPUT->footer();
     exit;
 }
diff --git a/grade/export/xml/lang/en/gradeexport_xml.php b/grade/export/xml/lang/en/gradeexport_xml.php
index 7cb8dbc6e8f..0cba69e75f3 100644
--- a/grade/export/xml/lang/en/gradeexport_xml.php
+++ b/grade/export/xml/lang/en/gradeexport_xml.php
@@ -26,3 +26,4 @@
 $string['pluginname'] = 'XML file';
 $string['xml:publish'] = 'Publish XML grade export';
 $string['xml:view'] = 'Use XML grade export';
+$string['useridnumberwarning'] = 'User\'s without an ID number are excluded from the XML export as they cannot be imported';
\ No newline at end of file
diff --git a/grade/lib.php b/grade/lib.php
index e04dccfdc46..392eed0d356 100644
--- a/grade/lib.php
+++ b/grade/lib.php
@@ -235,7 +235,6 @@ class graded_users_iterator {
         $result->user      = $user;
         $result->grades    = $grades;
         $result->feedbacks = $feedbacks;
-
         return $result;
     }
 
@@ -271,20 +270,20 @@ class graded_users_iterator {
     /**
      * _pop
      *
-     * @return void
+     * @return object current grade object
      */
     function _pop() {
         global $DB;
         if (empty($this->gradestack)) {
-            if (!$this->grades_rs) {
+            if (empty($this->grades_rs) || !$this->grades_rs->valid()) {
                 return null; // no grades present
             }
 
-            if ($this->grades_rs->next()) {
-                return null; // no more grades
-            }
+            $current = $this->grades_rs->current();
 
-            return $this->grades_rs->current();
+            $this->grades_rs->next();
+
+            return $current;
         } else {
             return array_pop($this->gradestack);
         }