diff --git a/mod/assignment/assignment.js b/mod/assignment/assignment.js
index 8615c4b..0df5909 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('select[name="grade"]');
+    if (gradeNode) {
+        var originalValue = gradeNode.get('value');
+        gradeNode.on('change', function() {
+            if (gradeNode.get('value') != originalValue) {
+                alert(M.str.mod_assignment.changegradewarning);
+            }
+        });
+    }
+};
diff --git a/mod/assignment/lang/en/assignment.php b/mod/assignment/lang/en/assignment.php
index bef1da4..b77b1e1 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'] = 'Warning: this assignment has graded submissions and changing the grade will not automatically re-calculate new submission grades. You must re-grade all submissions if you choose to continue.';
 $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 85c8423..313522c 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 +76,11 @@ class mod_assignment_mod_form extends moodleform_mod {
         $this->standard_coursemodule_elements();
 
         $this->add_action_buttons();
+
+        if (!empty($this->_instance) and $DB->record_exists_select('assignment_submissions', 'assignment = ? AND grade > -1', array($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);
+        }
     }
 
     // Needed by plugin assignment types if they include a filemanager element in the settings form