diff --git a/caravel/assets/javascripts/modules/caravel.js b/caravel/assets/javascripts/modules/caravel.js
index b6b881077eab..4d92951f1dbe 100644
--- a/caravel/assets/javascripts/modules/caravel.js
+++ b/caravel/assets/javascripts/modules/caravel.js
@@ -48,6 +48,7 @@ var color = function () {
     var seen = {};
     return function (s) {
       if (!s) { return; }
+      s = String(s);
       // next line is for caravel series that should have the same color
       s = s.replace('---', '');
       if (seen[s] === undefined) {