Just the method, not the property
diff --git a/system/database/DB_driver.php b/system/database/DB_driver.php
index 9869169..9e1c605 100644
--- a/system/database/DB_driver.php
+++ b/system/database/DB_driver.php
@@ -1208,7 +1208,7 @@
 	{
 		if ( ! is_bool($protect_identifiers))
 		{
-			$protect_identifiers = $this->protect_identifiers;
+			$protect_identifiers = $this->_protect_identifiers;
 		}
 
 		if (is_array($item))