[ci skip] Fix #5627
diff --git a/system/database/DB_driver.php b/system/database/DB_driver.php
index c397bb7..6350480 100644
--- a/system/database/DB_driver.php
+++ b/system/database/DB_driver.php
@@ -142,7 +142,7 @@
 	 *
 	 * @var	int
 	 */
-	public $port			= '';
+	public $port			= NULL;
 
 	/**
 	 * Persistent connection flag