diff --git a/grade/report/grader/index.php b/grade/report/grader/index.php
index 1174375775e..2e7022b7f82 100644
--- a/grade/report/grader/index.php
+++ b/grade/report/grader/index.php
@@ -191,6 +191,7 @@ if ($USER->gradeediting[$course->id] && ($report->get_pref('showquickfeedback')
     echo '<div>';
     echo '<input type="hidden" value="'.s($courseid).'" name="id" />';
     echo '<input type="hidden" value="'.sesskey().'" name="sesskey" />';
+    echo '<input type="hidden" value="'.time().'" name="timepageload" />';
     echo '<input type="hidden" value="grader" name="report"/>';
     echo '<input type="hidden" value="'.$page.'" name="page"/>';
     echo $reporthtml;
diff --git a/grade/report/grader/lib.php b/grade/report/grader/lib.php
index f9feea807d8..aa4a8edf28c 100644
--- a/grade/report/grader/lib.php
+++ b/grade/report/grader/lib.php
@@ -185,6 +185,7 @@ class grade_report_grader extends grade_report {
 
         // Were any changes made?
         $changedgrades = false;
+        $timepageload = clean_param($data->timepageload, PARAM_INT);
 
         foreach ($data as $varname => $students) {
 
@@ -259,8 +260,15 @@ class grade_report_grader extends grade_report {
                         }
 
                         $errorstr = '';
-                        // Warn if the grade is out of bounds.
-                        if (!is_null($finalgrade)) {
+                        $skip = false;
+
+                        $dategraded = $oldvalue->get_dategraded();
+                        if (!empty($dategraded) && $timepageload < $dategraded) {
+                            // Warn if the grade was updated while we were editing this form.
+                            $errorstr = 'gradewasmodifiedduringediting';
+                            $skip = true;
+                        } else if (!is_null($finalgrade)) {
+                            // Warn if the grade is out of bounds.
                             $bounded = $gradeitem->bounded_grade($finalgrade);
                             if ($bounded > $finalgrade) {
                                 $errorstr = 'lessthanmin';
@@ -268,6 +276,7 @@ class grade_report_grader extends grade_report {
                                 $errorstr = 'morethanmax';
                             }
                         }
+
                         if ($errorstr) {
                             $userfields = 'id, ' . get_all_user_name_fields(true);
                             $user = $DB->get_record('user', array('id' => $userid), $userfields);
@@ -275,6 +284,10 @@ class grade_report_grader extends grade_report {
                             $gradestr->username = fullname($user);
                             $gradestr->itemname = $gradeitem->get_name();
                             $warnings[] = get_string($errorstr, 'grades', $gradestr);
+                            if ($skip) {
+                                // Skipping the update of this grade it failed the tests above.
+                                continue;
+                            }
                         }
 
                     } else if ($datatype == 'feedback') {
diff --git a/lang/en/grades.php b/lang/en/grades.php
index 118d3663db4..769c54c408b 100644
--- a/lang/en/grades.php
+++ b/lang/en/grades.php
@@ -322,6 +322,7 @@ $string['gradetype_help'] = 'There are 4 grade types:
 Only value and scale grade types may be aggregated. The grade type for an activity-based grade item is set on the activity settings page.';
 $string['gradevaluetoobig'] = 'One of the grade values is larger than the allowed grade maximum of {$a}';
 $string['gradeview'] = 'View grade';
+$string['gradewasmodifiedduringediting'] = 'The grade entered for {$a->itemname} for {$a->username} was ignored because it was more recently updated by someone else.';
 $string['gradeweighthelp'] = 'Grade weight help';
 $string['groupavg'] = 'Group average';
 $string['hidden'] = 'Hidden';
diff --git a/lib/grade/grade_category.php b/lib/grade/grade_category.php
index b70030cead0..01a8449c577 100644
--- a/lib/grade/grade_category.php
+++ b/lib/grade/grade_category.php
@@ -628,6 +628,7 @@ class grade_category extends grade_object {
             $grade->finalgrade = null;
 
             if (!is_null($oldfinalgrade)) {
+                $grade->timemodified = time();
                 $success = $grade->update('aggregation');
 
                 // If successful trigger a user_graded event.
@@ -712,6 +713,7 @@ class grade_category extends grade_object {
             $grade->finalgrade = null;
 
             if (!is_null($oldfinalgrade)) {
+                $grade->timemodified = time();
                 $success = $grade->update('aggregation');
 
                 // If successful trigger a user_graded event.
@@ -754,6 +756,7 @@ class grade_category extends grade_object {
         if (grade_floats_different($grade->finalgrade, $oldfinalgrade) ||
                 grade_floats_different($grade->rawgrademax, $oldrawgrademax) ||
                 grade_floats_different($grade->rawgrademin, $oldrawgrademin)) {
+            $grade->timemodified = time();
             $success = $grade->update('aggregation');
 
             // If successful trigger a user_graded event.