Cannot use omen of the liege + preserved rib on ILVL 65 body armour

I've got a ILVL 65 Swiftstalker coat that I wanna try to get fire + chaos res on. The body armour has an open suffix so AFAIK the mod should fit.


When I try to use a preserved rib on the armour with a omen of the liege enabled I get "Omen is incompatible with this Desecrating item".

Am I missing something here? Can you only use ancient ribs with the omen of the liege?