diff --git a/src/script.php b/src/script.php
index cbe4db17..327e2208 100644
--- a/src/script.php
+++ b/src/script.php
@@ -210,10 +210,11 @@ class plgSystemMokoWaaSInstallerScript implements InstallerScriptInterface
 	}
 
 	/**
-	 * Ensure mokocassiopeia template is installed and locked.
+	 * Ensure the active Moko template is installed and locked.
 	 *
-	 * If the template exists in #__extensions, lock and protect it.
-	 * If not found, attempt to install from the update server.
+	 * Prefers MokoOnyx (successor). Falls back to MokoCassiopeia.
+	 * If MokoOnyx is found, lock it and unlock MokoCassiopeia.
+	 * If only MokoCassiopeia is found, lock it as before.
 	 *
 	 * @return  void
 	 *
@@ -221,17 +222,50 @@ class plgSystemMokoWaaSInstallerScript implements InstallerScriptInterface
 	 */
 	private function ensureMokoCassiopeia()
 	{
-		$db    = Factory::getDbo();
+		$db = Factory::getDbo();
+
+		// Check for MokoOnyx first (successor template)
 		$query = $db->getQuery(true)
 			->select([$db->quoteName('extension_id'), $db->quoteName('enabled')])
 			->from($db->quoteName('#__extensions'))
-			->where($db->quoteName('element') . ' = '
-				. $db->quote('mokocassiopeia'))
-			->where($db->quoteName('type') . ' = '
-				. $db->quote('template'));
+			->where($db->quoteName('element') . ' = ' . $db->quote('mokoonyx'))
+			->where($db->quoteName('type') . ' = ' . $db->quote('template'));
+		$onyx = $db->setQuery($query)->loadObject();
 
-		$db->setQuery($query);
-		$template = $db->loadObject();
+		if ($onyx)
+		{
+			// Lock and protect MokoOnyx
+			$db->setQuery(
+				$db->getQuery(true)
+					->update($db->quoteName('#__extensions'))
+					->set($db->quoteName('enabled') . ' = 1')
+					->set($db->quoteName('locked') . ' = 1')
+					->set($db->quoteName('protected') . ' = 1')
+					->where($db->quoteName('extension_id') . ' = ' . (int) $onyx->extension_id)
+			)->execute();
+
+			$this->setDefaultTemplate('mokoonyx', 0);
+
+			// Unlock MokoCassiopeia if present (allow uninstall)
+			$db->setQuery(
+				$db->getQuery(true)
+					->update($db->quoteName('#__extensions'))
+					->set($db->quoteName('locked') . ' = 0')
+					->set($db->quoteName('protected') . ' = 0')
+					->where($db->quoteName('element') . ' = ' . $db->quote('mokocassiopeia'))
+					->where($db->quoteName('type') . ' = ' . $db->quote('template'))
+			)->execute();
+
+			return;
+		}
+
+		// Fallback: MokoCassiopeia
+		$query = $db->getQuery(true)
+			->select([$db->quoteName('extension_id'), $db->quoteName('enabled')])
+			->from($db->quoteName('#__extensions'))
+			->where($db->quoteName('element') . ' = ' . $db->quote('mokocassiopeia'))
+			->where($db->quoteName('type') . ' = ' . $db->quote('template'));
+		$template = $db->setQuery($query)->loadObject();
 
 		if ($template)
 		{
@@ -247,7 +281,6 @@ class plgSystemMokoWaaSInstallerScript implements InstallerScriptInterface
 			);
 			$db->execute();
 
-			// Set as default site template
 			$this->setDefaultTemplate('mokocassiopeia', 0);
 
 			return;