Hey @shira! We actually don’t have a warning like that for stan_glmer(), so I think this warning is coming from one of the functions in the lme4 package that stan_glmer() is calling internally. We should probably be catching and suppressing that warning inside stan_glmer() but I hadn’t seen it before! I’ll open an issue at the rstanarm repository on GitHub and we’ll try to figure out if we can suppress it.