diff --git a/source/script.php b/source/script.php
index 5b9d10f7..7e46ce24 100644
--- a/source/script.php
+++ b/source/script.php
@@ -54,10 +54,36 @@ class Pkg_MokosuiteclientInstallerScript
 			$db->setQuery("ALTER TABLE " . $db->quoteName('#__extensions')
 				. " MODIFY " . $db->quoteName('element') . " VARCHAR(100) NOT NULL");
 			$db->execute();
+
+			// Delete orphaned rows with empty element (created by the old DEFAULT '')
+			$db->setQuery("DELETE FROM " . $db->quoteName('#__extensions')
+				. " WHERE " . $db->quoteName('element') . " = ''");
+			$db->execute();
+			$deleted = $db->getAffectedRows();
+
+			if ($deleted > 0)
+			{
+				Log::add("Deleted {$deleted} orphaned extension row(s) with empty element", Log::INFO, 'mokosuiteclient');
+			}
+
+			// Remove stale plugin files that leaked to group root
+			$staleFiles = [
+				JPATH_PLUGINS . '/system/services',
+				JPATH_PLUGINS . '/system/src',
+				JPATH_PLUGINS . '/system/language',
+			];
+
+			foreach ($staleFiles as $stale)
+			{
+				if (is_dir($stale))
+				{
+					$this->rmdirRecursive($stale);
+				}
+			}
 		}
 		catch (\Throwable $e)
 		{
-			// Non-fatal — column may already be correct
+			// Non-fatal
 		}
 	}