Here it is, I hope it helps somebody else.

$editFormAction = $_SERVER['PHP_SELF'];
if (isset($_SERVER['QUERY_STRING'])) {
  $editFormAction .= "?" . htmlentities($_SERVER['QUERY_STRING']);
}

if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "comments"))
 {
 
 $comment = htmlentities($_POST['comment']);
 
function check_field1($comment)
{
if (preg_match("/</", $comment))
{
return TRUE;
}
}
$error=0; 
if(check_field1($comment))
{
  
  $error++;
   $insertGoTo = "comments.php";
  if (isset($_SERVER['QUERY_STRING'])) {
    $insertGoTo .= (strpos($insertGoTo, '?')) ? "&" : "?";
    $insertGoTo .= $_SERVER['QUERY_STRING'];
  }
  header(sprintf("Location: %s", $insertGoTo)); // $error=$error+1;
}

if($error == 0)
   $insertSQL = sprintf("INSERT INTO comments (comment, `day`, `month`, `year`) VALUES (%s, %s, %s, %s)",
                       GetSQLValueString($_POST['comment'], "text"),
                       GetSQLValueString($_POST['day'], "int"),
                       GetSQLValueString($_POST['month'], "text"),
                       GetSQLValueString($_POST['year'], "int"));

  mysql_select_db($database_connection, $connection);
  $Result1 = mysql_query($insertSQL, $connection) or die(mysql_error());

  $insertGoTo = "comments.php";
  if (isset($_SERVER['QUERY_STRING'])) {
    $insertGoTo .= (strpos($insertGoTo, '?')) ? "&" : "?";
    $insertGoTo .= $_SERVER['QUERY_STRING'];
  }
  header(sprintf("Location: %s", $insertGoTo));
  }