diff --git a/js/src/tooltip.js b/js/src/tooltip.js
index 77803dc402..03d9e4cc8e 100644
--- a/js/src/tooltip.js
+++ b/js/src/tooltip.js
@@ -16,7 +16,7 @@ const Tooltip = (($) => {
    * Check for Tether dependency
    * Tether - http://github.hubspot.com/tether/
    */
-  if (window.Tether === undefined) {
+  if ('undefined' === typeof Tether) {
     throw new Error('Bootstrap tooltips require Tether (http://github.hubspot.com/tether/)')
   }