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
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index dc07881..ba24698 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -20,6 +20,7 @@
 -  Fixed a bug (#5587) - :doc:`Database Forge <database/forge>` method ``create_table()`` generated an ``E_WARNING`` message.
 -  Fixed a bug (#5590) - :doc:`Form Validation Library <libraries/form_validation>` rule **valid_base64** didn't have a default error message.
 -  Fixed a bug (#5624) - :doc:`Database Library <database/index>` methods ``list_fields()``, ``field_exists()`` returned incorrect results after tables are modified.
+-  Fixed a bug (#5627) - :doc:`Database <database/index>` driver 'mysqli' triggered an ``E_WARNING`` message if there's no ``'port'`` specified in the database configuration.
 
 Version 3.1.9
 =============