$CI->_remove_invisible_characters($str);

fixed to

$CI->input->_remove_invisible_characters($str);
diff --git a/system/database/drivers/oci8/oci8_driver.php b/system/database/drivers/oci8/oci8_driver.php
index b949a96..42dd517 100644
--- a/system/database/drivers/oci8/oci8_driver.php
+++ b/system/database/drivers/oci8/oci8_driver.php
@@ -375,7 +375,7 @@
 		// Access the CI object
 		$CI =& get_instance();
 
-		return $CI->_remove_invisible_characters($str);
+		return $CI->input->_remove_invisible_characters($str);
 	}
 
 	// --------------------------------------------------------------------
diff --git a/user_guide/changelog.html b/user_guide/changelog.html
index f48bb0b..06375d6 100644
--- a/user_guide/changelog.html
+++ b/user_guide/changelog.html
@@ -136,6 +136,7 @@
 			<li>Fixed a bug where TRUNCATE was not considered a "write" query (#6619).</li>
 			<li>Fixed a bug where csv_from_result() was checking for a nonexistent method.</li>
 			<li>Fixed a bug _protect_identifiers() where it was improperly removing all pipe symbols from items</li>
+			<li>Fixed a fatal error in the Oracle driver (#6752)</li>
 		</ul>
 	</li>
 	<li>Fixed assorted user guide typos or examples (#5998, #6093, #6259, #6339, #6432, #6521).</li>