Dual internet connection

Hi Guys,

We have Fortigate 50E with two ISPs

ISP1 <> WAN1 <> LAN1

ISP2 <> WAN2 <> LAN2

We have two subnets and each of them has dedicated ISP. Everything works propertly but I would like to extend this setup for full redundancy. For example if ISP1 is down ISP2 should deliver internet connection into LAN1 as well.

Is it possible to configure? How can I do it?

Regards,

W