Create Site-to-Site IPsec VPN Tunnel using V4.0 and V5.0 firmware

Our current network all have v4.0 firmware on our fortigates.  We have bought a new 60E(that has v5.4 firmware) and want to connect this one to our data center fortigate that is running v4.0 firmware.  Is there a procedure to create a VPN tunnel between v4.0 and v5.4 firmware?