Yellow Fever and Entry into Peru

Does anyone know if the Yellow Fever Certificate is required when entering Peru from Ecuador on a bus? I've heard mixed comments about this.

i've never taken the bus from ecuador to peru but i really doubt it..

1) peru doesn't require yellow fever certificates to enter the country

2) even in places where they are legally required to check for it, like landing in the Puerto Maldonado airport in the jungle, they don't check for it

yellow fever is a jungle thing, and if you're busing in then you're either crossing on the desert coastline or through a cloud-forest mountain area