diff --git a/event/main_listener.php b/event/main_listener.php
index b1a2f0c..07ed675 100644
--- a/event/main_listener.php
+++ b/event/main_listener.php
@@ -78,7 +78,7 @@ public static function getSubscribedEvents()
 	 * Constructor
 	 *
 	 * @param auth					$auth
-	 * @param config					$config
+	 * @param config				$config
 	 * @param db_text				$config_text
 	 * @param language				$language
 	 * @param template				$template
@@ -104,12 +104,22 @@ public function __construct(auth $auth, config $config, db_text $config_text, la
 	 */
 	public function add_custom_sites($event)
 	{
+		$is_phpbb4 = phpbb_version_compare($this->config['version'], '4.0.0-a1', '>=');
+		$phpbb4_builtins = array_flip([
+			'applepodcasts', 'bluesky', 'bunny', 'mastodon', 'pastebin', 'threads', 'twitter',
+		]);
+
 		foreach ($this->custom_sites->get_collection() as $site)
 		{
-			$event['configurator']->MediaEmbed->defaultSites->add(
-				basename($site, ext::YML),
-				Yaml::parse(file_get_contents($site))
-			);
+			$name = basename($site, ext::YML);
+
+			// Skip built-in sites when running phpBB 4
+			if ($is_phpbb4 && isset($phpbb4_builtins[$name]))
+			{
+				continue;
+			}
+
+			$event['configurator']->MediaEmbed->defaultSites->add($name, Yaml::parseFile($site));
 		}
 	}
 
diff --git a/tests/event/listener_test.php b/tests/event/listener_test.php
index a374862..b546447 100644
--- a/tests/event/listener_test.php
+++ b/tests/event/listener_test.php
@@ -189,10 +189,14 @@ public function test_configure_media_embed($tag, $code, $id, $exists, $parse_url
 	{
 		$this->custom_sites->expects(self::once())
 			->method('get_collection')
-			->willReturn([__DIR__ . '/../fixtures/sites/ok.yml']);
+			->willReturn([
+				__DIR__ . '/../fixtures/sites/ok.yml',
+				__DIR__ . '/../fixtures/sites/bluesky.yml',  // this is to test that phpbb4 filtering works
+			]);
 
 		// Update configs with test values
 		$this->config['media_embed_parse_urls'] = $parse_urls;
+		$this->config['version'] = '4.0.0'; // this is to test that phpbb4 filtering works
 
 		// Get the s9e configurator
 		$configurator = $this->container