diff --git a/grade/report/grader/index.php b/grade/report/grader/index.php
index 435fb5734d1..b9ff46a9458 100644
--- a/grade/report/grader/index.php
+++ b/grade/report/grader/index.php
@@ -160,6 +160,7 @@ 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 bebc6c22fbd..e54ace906ac 100644
--- a/grade/report/grader/lib.php
+++ b/grade/report/grader/lib.php
@@ -176,6 +176,7 @@ 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) {
 
@@ -250,10 +251,15 @@ class grade_report_grader extends grade_report {
                         }
 
                         $errorstr = '';
-                        // Warn if the grade is out of bounds.
-                        if (is_null($finalgrade)) {
-                            // ok
-                        } else {
+                        $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';
@@ -261,6 +267,7 @@ 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);
@@ -268,6 +275,10 @@ 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 119f00a0f26..4d5b485a017 100644
--- a/lang/en/grades.php
+++ b/lang/en/grades.php
@@ -302,6 +302,7 @@ $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.';
 $string['gradeview'] = 'View grade';
+$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 453294c183e..07f0b58e726 100644
--- a/lib/grade/grade_category.php
+++ b/lib/grade/grade_category.php
@@ -564,6 +564,7 @@ class grade_category extends grade_object {
             $grade->finalgrade = null;
 
             if (!is_null($oldfinalgrade)) {
+                $grade->timemodified = time();
                 $grade->update('aggregation');
             }
             return;
@@ -606,6 +607,7 @@ class grade_category extends grade_object {
             $grade->finalgrade = null;
 
             if (!is_null($oldfinalgrade)) {
+                $grade->timemodified = time();
                 $grade->update('aggregation');
             }
             return;
@@ -622,6 +624,7 @@ class grade_category extends grade_object {
 
         // update in db if changed
         if (grade_floats_different($grade->finalgrade, $oldfinalgrade)) {
+            $grade->timemodified = time();
             $grade->update('aggregation');
         }
 
@@ -897,6 +900,7 @@ class grade_category extends grade_object {
 
         // update in db if changed
         if (grade_floats_different($grade->finalgrade, $oldfinalgrade)) {
+            $grade->timemodified = time();
             $grade->update('aggregation');
         }