diff --git a/Services/HtmlSanitiser.php b/Services/HtmlSanitiser.php
index 3c5eb31..c26f93b 100644
--- a/Services/HtmlSanitiser.php
+++ b/Services/HtmlSanitiser.php
@@ -97,8 +97,10 @@ class HtmlSanitiser
         $config->set('HTML.Nofollow', true);
         $config->set('HTML.TargetNoopener', true);
 
-        // Disable cache to allow custom HTML definitions
+        // Disable cache and set definition ID for custom HTML definitions
         $config->set('Cache.DefinitionImpl', null);
+        $config->set('HTML.DefinitionID', 'core-content-html5');
+        $config->set('HTML.DefinitionRev', 1);
 
         // Register HTML5 elements that HTMLPurifier doesn't know about
         if ($def = $config->maybeGetRawHTMLDefinition()) {
diff --git a/tests/TestCase.php b/tests/TestCase.php
index 4e09424..36fd62f 100644
--- a/tests/TestCase.php
+++ b/tests/TestCase.php
@@ -27,5 +27,10 @@ abstract class TestCase extends BaseTestCase
             'database' => ':memory:',
             'prefix' => '',
         ]);
+
+        // Stub external dependencies not available in test environment
+        if (! class_exists(\Plug\Cdn\CdnManager::class)) {
+            $app->bind(\Plug\Cdn\CdnManager::class, fn () => new class {});
+        }
     }
 }