From Marriott T&C:

"Guaranteed Room Type: Guaranteed priority for your requested type of room. Subject to availability at participating locations worldwide when your qualifying Elite level and specific preference are noted on the reservation for your stay. (Pillow, room location, extra bed, crib requests, etc. are not included in Guarantee.) Outside U.S. and Canada: smoking/non-smoking preferences may also be given priority, based on availability; exact bed sizes may vary and only Platinum members will have guaranteed priority for your requested type of bed and room. Not available at Marriott Vacation Club."

Cheers.