function(facet, path) {
    if (this.isHierarchicalFacetRefined(facet)) {
      throw new Error(facet + ' is already refined.');
    }
    var mod = {};
    mod[facet] = [path];
    return this.setQueryParameters({
      hierarchicalFacetsRefinements: defaults({}, mod, this.hierarchicalFacetsRefinements)
    });
  }