# Multilevel model where an interaction is a varying slope

I have a multilevel problem where I want to have a random intercept and a random slope. However the random slope is the interaction of two predictors. In this case, do I also have to allow random slopes for the individual predictors?

For example, with lme4 is this OK?

lmer(y ~ x + w + x:w + (1 + x:w|group), data=mydata)

Or should i use

lmer(y ~ x + w + x:w + (1 + x + w + x:w|group), data=mydata)

even if I am not interested in either x or w to be random?