diff --git a/addons/web_graph/static/src/js/pivot.js b/addons/web_graph/static/src/js/pivot.js
index bca759a13e5..38dad2c33cb 100644
--- a/addons/web_graph/static/src/js/pivot.js
+++ b/addons/web_graph/static/src/js/pivot.js
@@ -232,6 +232,9 @@ openerp.web_graph.PivotTable = openerp.web.Class.extend({
 	},
 
 	update_headers: function (root, new_headers) {
+		if (!root.main) {
+			return this.expand_headers(root, new_headers);
+		}
 		_.each(root.headers, function (header) {
 			var corresponding_header = _.find(new_headers, function (h) {
 				return _.isEqual(h.path, header.path);