diff --git a/mod/assignment/assignment.js b/mod/assignment/assignment.js
index 8615c4bd466..8a5844087d5 100644
--- a/mod/assignment/assignment.js
+++ b/mod/assignment/assignment.js
@@ -35,3 +35,15 @@ M.mod_assignment.init_tree = function(Y, expand_all, htmlid) {
         tree.render();
     });
 };
+
+M.mod_assignment.init_grade_change = function(Y) {
+    var gradenode = Y.one('#id_grade');
+    if (gradenode) {
+        var originalvalue = gradenode.get('value');
+        gradenode.on('change', function() {
+            if (gradenode.get('value') != originalvalue) {
+                alert(M.str.mod_assignment.changegradewarning);
+            }
+        });
+    }
+};
\ No newline at end of file
diff --git a/mod/assignment/lang/en/assignment.php b/mod/assignment/lang/en/assignment.php
index bef1da47f3c..3860ff10c15 100644
--- a/mod/assignment/lang/en/assignment.php
+++ b/mod/assignment/lang/en/assignment.php
@@ -55,6 +55,7 @@ $string['assignment:view'] = 'View assignment';
 $string['availabledate'] = 'Available from';
 $string['cannotdeletefiles'] = 'An error occurred and files could not be deleted';
 $string['cannotviewassignment'] = 'You can not view this assignment';
+$string['changegradewarning'] = 'This assignment has graded submissions and changing the grade will not automatically re-calculate existing submission grades. You must re-grade all existing submissions, if you wish to change the grade.';
 $string['comment'] = 'Comment';
 $string['commentinline'] = 'Comment inline';
 $string['commentinline_help'] = 'If enabled, the submission text will be copied into the feedback comment field during grading, making it easier to comment inline (using a different colour, perhaps) or to edit the original text.';
diff --git a/mod/assignment/mod_form.php b/mod/assignment/mod_form.php
index 85c84238a1f..56b407d6ea6 100644
--- a/mod/assignment/mod_form.php
+++ b/mod/assignment/mod_form.php
@@ -9,7 +9,7 @@ class mod_assignment_mod_form extends moodleform_mod {
     protected $_assignmentinstance = null;
 
     function definition() {
-        global $CFG, $DB;
+        global $CFG, $DB, $PAGE;
         $mform =& $this->_form;
 
         // this hack is needed for different settings of each subtype
@@ -76,6 +76,21 @@ class mod_assignment_mod_form extends moodleform_mod {
         $this->standard_coursemodule_elements();
 
         $this->add_action_buttons();
+
+        // Add warning popup/noscript tag, if grades are changed by user.
+        if ($mform->elementExists('grade') && !empty($this->_instance) && $DB->record_exists_select('assignment_submissions', 'assignment = ? AND grade <> -1', array($this->_instance))) {
+            $module = array(
+                'name' => 'mod_assignment',
+                'fullpath' => '/mod/assignment/assignment.js',
+                'requires' => array('node', 'event'),
+                'strings' => array(array('changegradewarning', 'mod_assignment'))
+                );
+            $PAGE->requires->js_init_call('M.mod_assignment.init_grade_change', null, false, $module);
+
+            // Add noscript tag in case
+            $noscriptwarning = $mform->createElement('static', 'warning', null,  html_writer::tag('noscript', get_string('changegradewarning', 'mod_assignment')));
+            $mform->insertElementBefore($noscriptwarning, 'grade');
+        }
     }
 
     // Needed by plugin assignment types if they include a filemanager element in the settings form