diff --git a/lib/questionlib.php b/lib/questionlib.php
index c0771b4a5d3..b292ee06392 100644
--- a/lib/questionlib.php
+++ b/lib/questionlib.php
@@ -1306,10 +1306,11 @@ function question_categorylist($categoryid): array {
     global $DB;
 
     // Final list of category IDs.
-    $categorylist = array();
+    $categorylist = [];
 
     // A list of category IDs to check for any sub-categories.
-    $subcategories = array($categoryid);
+    $subcategories = [$categoryid];
+    $contextid = $DB->get_field('question_categories', 'contextid', ['id' => $categoryid]);
 
     while ($subcategories) {
         foreach ($subcategories as $subcategory) {
@@ -1320,37 +1321,40 @@ function question_categorylist($categoryid): array {
             $categorylist[$subcategory] = $subcategory;
         }
 
-        list ($in, $params) = $DB->get_in_or_equal($subcategories);
+        [$in, $params] = $DB->get_in_or_equal($subcategories);
+        $params[] = $contextid;
 
-        $subcategories = $DB->get_records_select_menu('question_categories', "parent $in", $params,
-                                                    null, 'id,id AS id2');
+        // Order by id is not strictly needed, but it will be cheap, and makes the results deterministic.
+        $subcategories = $DB->get_records_select_menu('question_categories',
+                "parent $in AND contextid = ?", $params, 'id', 'id,id AS id2');
     }
 
     return $categorylist;
 }
 
 /**
- * Get all parent categories of a given question category in decending order.
+ * Get all parent categories of a given question category in descending order.
+ *
  * @param int $categoryid for which you want to find the parents.
  * @return array of question category ids of all parents categories.
  */
 function question_categorylist_parents(int $categoryid): array {
     global $DB;
-    $parent = $DB->get_field('question_categories', 'parent', array('id' => $categoryid));
-    if (!$parent) {
-        return [];
-    }
-    $categorylist = [$parent];
-    $currentid = $parent;
-    while ($currentid) {
-        $currentid = $DB->get_field('question_categories', 'parent', array('id' => $currentid));
-        if ($currentid) {
-            $categorylist[] = $currentid;
+
+    $category = $DB->get_record('question_categories', ['id' => $categoryid]);
+    $contextid = $category->contextid;
+
+    $categorylist = [];
+    while ($category->parent) {
+        $category = $DB->get_record('question_categories', ['id' => $category->parent]);
+        if (!$category || $category->contextid != $contextid) {
+            break;
         }
+        $categorylist[] = $category->id;
     }
-    // Present the list in decending order (the top category at the top).
-    $categorylist = array_reverse($categorylist);
-    return $categorylist;
+
+    // Present the list in descending order (the top category at the top).
+    return array_reverse($categorylist);
 }
 
 // Import/Export Functions.
diff --git a/lib/tests/questionlib_test.php b/lib/tests/questionlib_test.php
index fdec7014422..7c6cc9c98fc 100644
--- a/lib/tests/questionlib_test.php
+++ b/lib/tests/questionlib_test.php
@@ -2009,9 +2009,73 @@ class questionlib_test extends \advanced_testcase {
     }
 
     /**
-     * Test of question_categorylist_parents function.
+     * Test of question_categorylist function.
+     *
+     * @covers ::question_categorylist()
      */
-    public function test_question_categorylist_parents() {
+    public function test_question_categorylist(): void {
+        $this->resetAfterTest();
+
+        // Create a category tree.
+        /** @var \core_question_generator $questiongenerator */
+        $questiongenerator = $this->getDataGenerator()->get_plugin_generator('core_question');
+        $context = \context_system::instance();
+
+        $top = question_get_top_category($context->id, true);
+        $cat1 = $questiongenerator->create_question_category(['parent' => $top->id]);
+        $sub11 = $questiongenerator->create_question_category(['parent' => $cat1->id]);
+        $sub12 = $questiongenerator->create_question_category(['parent' => $cat1->id]);
+        $cat2 = $questiongenerator->create_question_category(['parent' => $top->id]);
+        $sub22 = $questiongenerator->create_question_category(['parent' => $cat2->id]);
+
+        // Test - returned array has keys and values the same.
+        $this->assertEquals([$sub22->id], array_keys(question_categorylist($sub22->id)));
+        $this->assertEquals([$sub22->id], array_values(question_categorylist($sub22->id)));
+        $this->assertEquals([$cat1->id, $sub11->id, $sub12->id], array_keys(question_categorylist($cat1->id)));
+        $this->assertEquals([$cat1->id, $sub11->id, $sub12->id], array_values(question_categorylist($cat1->id)));
+        $this->assertEquals([$top->id, $cat1->id, $cat2->id, $sub11->id, $sub12->id, $sub22->id],
+                array_keys(question_categorylist($top->id)));
+        $this->assertEquals([$top->id, $cat1->id, $cat2->id, $sub11->id, $sub12->id, $sub22->id],
+                array_values(question_categorylist($top->id)));
+    }
+
+    /**
+     * Test of question_categorylist function when there is bad data, with a category pointing to a parent in another context.
+     *
+     * This is a situation that should never arise (parents and their children should always belong to the same context)
+     * but it does, because bugs, so the code should be robust to it.
+     *
+     * @covers ::question_categorylist()
+     */
+    public function test_question_categorylist_bad_data(): void {
+        $this->resetAfterTest();
+
+        // Create a category tree.
+        $course = $this->getDataGenerator()->create_course();
+        $coursecontext = \context_course::instance($course->id);
+        /** @var \core_question_generator $questiongenerator */
+        $questiongenerator = $this->getDataGenerator()->get_plugin_generator('core_question');
+        $context = \context_system::instance();
+
+        $top = question_get_top_category($context->id, true);
+        $cat1 = $questiongenerator->create_question_category(['parent' => $top->id]);
+        $sub11 = $questiongenerator->create_question_category(['parent' => $cat1->id]);
+        $sub12 = $questiongenerator->create_question_category(['parent' => $cat1->id]);
+        $cat2 = $questiongenerator->create_question_category(['parent' => $top->id, 'contextid' => $coursecontext->id]);
+        $sub22 = $questiongenerator->create_question_category(['parent' => $cat2->id]);
+
+        // Test - returned array has keys and values the same.
+        $this->assertEquals([$cat2->id, $sub22->id], array_keys(question_categorylist($cat2->id)));
+        $this->assertEquals([$top->id, $cat1->id, $sub11->id, $sub12->id],
+                array_keys(question_categorylist($top->id)));
+    }
+
+    /**
+     * Test of question_categorylist_parents function.
+     *
+     * @covers ::question_categorylist_parents()
+     */
+    public function test_question_categorylist_parents(): void {
         $this->resetAfterTest();
         $generator = $this->getDataGenerator();
         /** @var \core_question_generator $questiongenerator */
@@ -2023,11 +2087,36 @@ class questionlib_test extends \advanced_testcase {
         // Add sub-categories.
         $cat1 = $questiongenerator->create_question_category(['parent' => $cat0->id]);
         $cat2 = $questiongenerator->create_question_category(['parent' => $cat1->id]);
+
         // Test the 'get parents' function.
-        $parentcategories = question_categorylist_parents($cat2->id);
-        $this->assertEquals($cat0->id, $parentcategories[0]);
-        $this->assertEquals($cat1->id, $parentcategories[1]);
-        $this->assertCount(2, $parentcategories);
+        $this->assertEquals([$cat0->id, $cat1->id], question_categorylist_parents($cat2->id));
+    }
+
+    /**
+     * Test question_categorylist_parents when there is bad data, with a category pointing to a parent in another context.
+     *
+     * This is a situation that should never arise (parents and their children should always belong to the same context)
+     * but it does, because bugs, so the code should be robust to it.
+     *
+     * @covers ::question_categorylist_parents()
+     */
+    public function test_question_categorylist_parents_bad_data(): void {
+        $this->resetAfterTest();
+        $generator = $this->getDataGenerator();
+        /** @var \core_question_generator $questiongenerator */
+        $questiongenerator = $generator->get_plugin_generator('core_question');
+        $category = $generator->create_category();
+        $context = \context_coursecat::instance($category->id);
+        // Create a top category.
+        $cat0 = question_get_top_category($context->id, true);
+        // Add sub-categories - but in a different context.
+        $cat1 = $questiongenerator->create_question_category(
+            ['parent' => $cat0->id, 'contextid' => \context_system::instance()->id]);
+        $cat2 = $questiongenerator->create_question_category(
+            ['parent' => $cat1->id, 'contextid' => \context_system::instance()->id]);
+
+        // Test the 'get parents' function only returns categories in the same context.
+        $this->assertEquals([$cat1->id], question_categorylist_parents($cat2->id));
     }
 
     /**
diff --git a/question/tests/generator/lib.php b/question/tests/generator/lib.php
index a1d3deb6be8..3269428ef58 100644
--- a/question/tests/generator/lib.php
+++ b/question/tests/generator/lib.php
@@ -69,7 +69,11 @@ class core_question_generator extends component_generator_base {
         $record = $this->datagenerator->combine_defaults_and_record($defaults, $record);
 
         if (!isset($record['contextid'])) {
-            $record['contextid'] = context_system::instance()->id;
+            if (isset($record['parent'])) {
+                $record['contextid'] = $DB->get_field('question_categories', 'contextid', ['id' => $record['parent']]);
+            } else {
+                $record['contextid'] = context_system::instance()->id;
+            }
         }
         if (!isset($record['parent'])) {
             $record['parent'] = question_get_top_category($record['contextid'], true)->id;