When I carried a full size pillow, I think there was never an issue (with it being an extra carry on) because it was obvious why I needed it and I used it and it was never in the overhead. When I travel with a travel pillow and blanket (for longer flights), those always fit in my acceptable carry ons. Basically, I think it comes down to what tfar basically said in that if you are only putting one bag up, it shouldn't be an issue.