diff --git a/grade/edit/tree/item.php b/grade/edit/tree/item.php
index 7acf2ebe17d..b3399ddc815 100644
--- a/grade/edit/tree/item.php
+++ b/grade/edit/tree/item.php
@@ -132,7 +132,7 @@ if ($mform->is_cancelled()) {
     unset($data->locked);
     unset($data->locktime);
 
-    $convert = array('grademax', 'grademin', 'gradepass', 'multfactor', 'plusfactor', 'aggregationcoef');
+    $convert = array('grademax', 'grademin', 'gradepass', 'multfactor', 'plusfactor', 'aggregationcoef', 'aggregationcoef2');
     foreach ($convert as $param) {
         if (property_exists($data, $param)) {
             $data->$param = unformat_float($data->$param);
@@ -148,6 +148,16 @@ if ($mform->is_cancelled()) {
         $grade_item->decimals = null;
     }
 
+    // Change weightoverride flag.
+    if (!isset($data->weightoverride)) {
+        $data->weightoverride = 0; // Checkbox unticked.
+    }
+    // If we are using natural weight and the weight has been un-overriden, force parent category to recalculate weights.
+    if ($grade_item->weightoverride != $data->weightoverride && $parent_category->aggregation == GRADE_AGGREGATE_SUM) {
+        $parent_category->force_regrading();
+    }
+    $grade_item->weightoverride = $data->weightoverride;
+
     if (empty($grade_item->id)) {
         $grade_item->itemtype = 'manual'; // all new items to be manual only
         $grade_item->insert();
diff --git a/grade/edit/tree/item_form.php b/grade/edit/tree/item_form.php
index 13ad68703c9..5ec14799594 100644
--- a/grade/edit/tree/item_form.php
+++ b/grade/edit/tree/item_form.php
@@ -97,6 +97,14 @@ class edit_item_form extends moodleform {
             $mform->setType('grademin', PARAM_RAW);
         }
 
+        $mform->addElement('checkbox', 'weightoverride', get_string('adjustedweight', 'grades'));
+        $mform->addHelpButton('weightoverride', 'weightoverride', 'grades');
+
+        $mform->addElement('text', 'aggregationcoef2', get_string('weight', 'grades'));
+        $mform->addHelpButton('aggregationcoef2', 'weight', 'grades');
+        $mform->setType('aggregationcoef2', PARAM_RAW);
+        $mform->hardFreeze('aggregationcoef2');
+
         $mform->addElement('text', 'gradepass', get_string('gradepass', 'grades'));
         $mform->addHelpButton('gradepass', 'gradepass', 'grades');
         $mform->disabledIf('gradepass', 'gradetype', 'eq', GRADE_TYPE_NONE);
@@ -295,6 +303,17 @@ class edit_item_form extends moodleform {
                 $mform->disabledIf('aggregationcoef', 'parentcategory', 'eq', $parent_category->id);
             }
 
+            // Remove fields used by natural weighting if the parent category is not using natural weighting.
+            if ($parent_category->aggregation != GRADE_AGGREGATE_SUM) {
+                print_object('removing');
+                if ($mform->elementExists('weightoverride')) {
+                    $mform->removeElement('weightoverride');
+                }
+                if ($mform->elementExists('aggregationcoef2')) {
+                    $mform->removeElement('aggregationcoef2');
+                }
+            }
+
             if ($category = $grade_item->get_item_category()) {
                 if ($category->aggregation == GRADE_AGGREGATE_SUM) {
                     if ($mform->elementExists('gradetype')) {
diff --git a/lang/en/grades.php b/lang/en/grades.php
index 3b43a88bc7e..a8ab8781137 100644
--- a/lang/en/grades.php
+++ b/lang/en/grades.php
@@ -35,6 +35,7 @@ $string['addoutcome'] = 'Add an outcome';
 $string['addoutcomeitem'] = 'Add outcome item';
 $string['addscale'] = 'Add a scale';
 $string['adjusted'] = 'Adjusted';
+$string['adjustedweight'] = 'Weight adjusted';
 $string['aggregateextracreditmean'] = 'Mean of grades (with extra credits)';
 $string['aggregatemax'] = 'Highest grade';
 $string['aggregatemean'] = 'Mean of grades';
@@ -711,9 +712,12 @@ $string['viewbygroup'] = 'Group';
 $string['viewgrades'] = 'View grades';
 $string['warningexcludedsum'] = 'Warning: excluding of grades is not compatible with sum aggregation.';
 $string['weight'] = 'weight';
+$string['weight_help'] = 'A value used to determine the relative value of multiple grade items in a category or course.';
 $string['weightcourse'] = 'Use weighted grades for course';
 $string['weightedascending'] = 'Sort by weighted percent ascending';
 $string['weighteddescending'] = 'Sort by weighted percent descending';
+$string['weightoverride'] = 'weight adjustment';
+$string['weightoverride_help'] = 'Uncheck this to reset a grade item weight to its automatically calculated value. Checking this will prevent the weight being automatically adjusted.';
 $string['weightedpct'] = 'weighted %';
 $string['weightedpctcontribution'] = 'weighted % contribution';
 $string['weightorextracredit'] = 'Weight or extra credit';
diff --git a/lib/grade/grade_category.php b/lib/grade/grade_category.php
index 9ec498eace1..9fc10681b30 100644
--- a/lib/grade/grade_category.php
+++ b/lib/grade/grade_category.php
@@ -1031,7 +1031,6 @@ class grade_category extends grade_object {
 
     /**
      * Recalculate the weights of the grade items in this category.
-     * THIS DOES NOT TAKE INTO ACCOUNT HIDDEN ACTIVITIES, GROUPS.
      */
     private function auto_update_weights() {
         if ($this->aggregation != GRADE_AGGREGATE_SUM) {