Added the missing "is" in the comment
diff --git a/system/libraries/Form_validation.php b/system/libraries/Form_validation.php
index 9efa9f3..2bebd2f 100644
--- a/system/libraries/Form_validation.php
+++ b/system/libraries/Form_validation.php
@@ -608,7 +608,7 @@
// Set the message type
$type = in_array('required', $rules) ? 'required' : 'isset';
- // Check if a custom message defined
+ // Check if a custom message is defined
if (isset($this->_field_data[$row['field']]['error_msg'][$type]))
{
$line = $this->_field_data[$row['field']]['error_msg'][$type];