diff --git a/lib/db/upgrade.php b/lib/db/upgrade.php
index d38e44b8c3d..aba5d839c28 100644
--- a/lib/db/upgrade.php
+++ b/lib/db/upgrade.php
@@ -1687,5 +1687,15 @@ function xmldb_main_upgrade($oldversion) {
         upgrade_main_savepoint(true, 2012120303.02);
     }
 
+    if ($oldversion < 2012120301.18) {
+        // MDL-29877 Some bad restores created grade items with no category information.
+        $sql = "UPDATE mdl_grade_items
+                   SET categoryid = courseid
+                 WHERE itemtype <> 'course' and itemtype <> 'category'
+                       AND categoryid IS NULL";
+        $DB->execute($sql);
+        upgrade_main_savepoint(true, 2012120301.18);
+    }
+
     return true;
 }
diff --git a/lib/grade/grade_category.php b/lib/grade/grade_category.php
index 87c494ffe26..1597d697a6d 100644
--- a/lib/grade/grade_category.php
+++ b/lib/grade/grade_category.php
@@ -1154,13 +1154,17 @@ class grade_category extends grade_object {
 
             } else {
                 $categoryid = $item->categoryid;
+                if (empty($categoryid)) {
+                    debugging('Found a grade item that isnt in a category');
+                } 
             }
 
             // prevent problems with duplicate sortorders in db
             $sortorder = $item->sortorder;
 
-            while (array_key_exists($sortorder, $cats[$categoryid]->children)) {
-                //debugging("$sortorder exists in item loop");
+            while (array_key_exists($categoryid, $cats)
+               && array_key_exists($sortorder, $cats[$categoryid]->children)) {
+
                 $sortorder++;
             }