Web-to-lead Required Fields

Web-to-lead Required Fields

Hi,
I recently integrated a contact form on my site with Zoho CRM with the web-to-lead feature. It works nicely; however, the issue I have is there doesn't seem to be a way to make certain fields required. Is this possible? I've already started getting messages with no first or last name, which makes the whole thing kind of pointless.
Any insight on how to make required fields would be greatly appreciated.

Thanks!
Chris