diff --git a/lib/db/caches.php b/lib/db/caches.php
index 6dbdc1e2fba..f5d59488af5 100644
--- a/lib/db/caches.php
+++ b/lib/db/caches.php
@@ -271,10 +271,13 @@ $definitions = array(
         'staticaccelerationsize' => 3
     ),
 
-    // Grade categories. Stored at request level as invalidation is very aggressive.
+    // Grade categories. Stored at session level as invalidation is very aggressive.
     'grade_categories' => array(
-        'mode' => cache_store::MODE_REQUEST,
+        'mode' => cache_store::MODE_SESSION,
         'simplekeys' => true,
+        'invalidationevents' => array(
+            'changesingradecategories',
+        )
     ),
 
     // Store temporary tables information.
diff --git a/lib/grade/grade_category.php b/lib/grade/grade_category.php
index 13d15c4b425..2723f7079a1 100644
--- a/lib/grade/grade_category.php
+++ b/lib/grade/grade_category.php
@@ -2691,7 +2691,6 @@ class grade_category extends grade_object {
      * @return void
      */
     public static function clean_record_set() {
-        $cache = cache::make('core', 'grade_categories');
-        $cache->purge();
+        cache_helper::purge_by_event('changesingradecategories');
     }
 }