diff --git a/addons/web_graph/static/src/js/graph.js b/addons/web_graph/static/src/js/graph.js
index 55ce776fa60..a84bb53fc85 100644
--- a/addons/web_graph/static/src/js/graph.js
+++ b/addons/web_graph/static/src/js/graph.js
@@ -5,6 +5,7 @@
 openerp.web_graph = function (instance) {
 
 var _lt = instance.web._lt;
+var _t = instance.web._t;
 
 // removed ``undefined`` values
 var filter_values = function (o) {
@@ -365,7 +366,7 @@ instance.web_graph.GraphView = instance.web.View.extend({
         }).then(function() {
             var res = {
                 'data': result,
-                'ticks': _.map(ticks, function(el, key) { return [el, key] })
+                'ticks': _.map(ticks, function(el, key) { return [el, key || _t("Undefined")] })
             };
             return res;
         }));