diff --git a/combo/public/static/js/combo.public.js b/combo/public/static/js/combo.public.js
index aff535f5..46cbe727 100644
--- a/combo/public/static/js/combo.public.js
+++ b/combo/public/static/js/combo.public.js
@@ -29,6 +29,7 @@ function combo_load_cell(elem) {
           },
           error: function(error) {
               var msg = $(elem).data('ajax-cell-error-message');
+              if (!msg) msg = 'Unknown error (code: ' + error.status + ')';
               $elem
                   .find('.loading')
                   .addClass('error-loading')