diff --git a/mod/quiz/editrandom.php b/mod/quiz/editrandom.php
index b0412d16e03..416f172ef71 100644
--- a/mod/quiz/editrandom.php
+++ b/mod/quiz/editrandom.php
@@ -23,6 +23,7 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+use core_question\question_reference_manager;
 use mod_quiz\quiz_settings;
 use mod_quiz\question\bank\random_question_view;
 
@@ -56,6 +57,7 @@ $PAGE->add_body_class('limitedwidth');
 $setreference = $DB->get_record('question_set_references',
     ['itemid' => $slot->id, 'component' => 'mod_quiz', 'questionarea' => 'slot']);
 $filterconditions = json_decode($setreference->filtercondition, true);
+$filterconditions = question_reference_manager::convert_legacy_set_reference_filter_condition($filterconditions);
 
 $params = $filterconditions;
 $params['cmid'] = $cm->id;
diff --git a/question/classes/question_reference_manager.php b/question/classes/question_reference_manager.php
index f3bd6c5c1ed..284e8e50e6a 100644
--- a/question/classes/question_reference_manager.php
+++ b/question/classes/question_reference_manager.php
@@ -86,6 +86,7 @@ class question_reference_manager {
      * @return array Post-4.3 filter condition.
      */
     public static function convert_legacy_set_reference_filter_condition(array $filtercondition): array {
+        global $DB;
         if (!isset($filtercondition['filter'])) {
             $filtercondition['filter'] = [];
 
@@ -96,8 +97,6 @@ class question_reference_manager {
                     'values' => [$filtercondition['questioncategoryid']],
                     'filteroptions' => ['includesubcategories' => $filtercondition['includingsubcategories']],
                 ];
-                unset($filtercondition['questioncategoryid']);
-                unset($filtercondition['includingsubcategories']);
             }
 
             // Tag filters.
@@ -115,10 +114,20 @@ class question_reference_manager {
                 unset($filtercondition['tags']);
             }
             // Add additional default properties to the filtercondition.
+            if (isset($filtercondition['questioncategoryid'])) {
+                $category = $DB->get_record('question_categories', ['id' => $filtercondition['questioncategoryid']]);
+                if ($category) {
+                    $filtercondition['cat'] = "{$category->id},{$category->contextid}";
+                } else {
+                    $filtercondition['cat'] = '';
+                }
+            }
             $filtercondition['tabname'] = 'questions';
             $filtercondition['qpage'] = 0;
             $filtercondition['qperpage'] = 100;
             $filtercondition['jointype'] = \core\output\datafilter::JOINTYPE_ALL;
+            unset($filtercondition['questioncategoryid']);
+            unset($filtercondition['includingsubcategories']);
         } else if (isset($filtercondition['filter']['category']['includesubcategories'])) {
             $filtercondition['filter']['category']['filteroptions'] =
                 ['includesubcategories' => $filtercondition['filter']['category']['includesubcategories']];
diff --git a/question/tests/legacy_question_set_conversion_test.php b/question/tests/legacy_question_set_conversion_test.php
new file mode 100644
index 00000000000..7a872975021
--- /dev/null
+++ b/question/tests/legacy_question_set_conversion_test.php
@@ -0,0 +1,78 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+namespace core_question;
+
+/**
+ * Test the conversion of legacy random question sets into the newer format.
+ *
+ * @package    core_question
+ * @copyright  2025 onwards Catalyst IT {@link http://www.catalyst-eu.net/}
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @author     Conn Warwicker <conn.warwicker@catalyst-eu.net>
+ * @covers     \core_question\question_reference_manager
+ */
+final class legacy_question_set_conversion_test extends \advanced_testcase {
+
+    /**
+     * Test the conversion of the old formatted `filtercondition` value to the newer format.
+     * @covers \core_question\question_reference_manager::convert_legacy_set_reference_filter_condition
+     * @return void
+     */
+    public function test_legacy_question_set_conversion(): void {
+
+        $this->resetAfterTest(false);
+
+        // Test conversion without a valid question category.
+        $old = [
+            'questioncategoryid' => 123,
+            'includingsubcategories' => 0,
+        ];
+
+        $new = question_reference_manager::convert_legacy_set_reference_filter_condition($old);
+        $expected = [
+            'filter' => [
+                'category' => [
+                    'jointype' => 1,
+                    'values' => [123],
+                    'filteroptions' => [
+                        'includesubcategories' => 0,
+                    ],
+                ],
+            ],
+            'cat' => '',
+            'tabname' => 'questions',
+            'qpage' => 0,
+            'qperpage' => 100,
+            'jointype' => 2,
+        ];
+        $this->assertEquals($new, $expected);
+
+        // Test conversion with a valid question category.
+        // Generate a question category.
+        $questiongenerator = $this->getDataGenerator()->get_plugin_generator('core_question');
+        $cat = $questiongenerator->create_question_category();
+
+        // Add the valid category into the arrays.
+        $old['questioncategoryid'] = $cat->id;
+        $expected['cat'] = "{$cat->id},{$cat->contextid}";
+        $expected['filter']['category']['values'] = [$cat->id];
+        $new = question_reference_manager::convert_legacy_set_reference_filter_condition($old);
+        $this->assertEquals($new, $expected);
+
+    }
+
+}