Does anyone know how to keep the IKEA Slatthult wall stickers from peeling off the wall?

I just got the ones that are orange and have things such as "nice" and "super" and "wow" on them and I put them on my wall, which I think is just painted drywall and I am sure it is clean. I put them on and they keep peeling at the edges and corners and every now and them, almost completely fall off the wall. Does anyone know how to keep them on?