diff --git a/lib/ical/timezone_service.js b/lib/ical/timezone_service.js
index 65fe55f6..cfd8dd57 100644
--- a/lib/ical/timezone_service.js
+++ b/lib/ical/timezone_service.js
@@ -57,8 +57,8 @@ const TimezoneService = {
   /**
    * Returns a timezone by its tzid if present.
    *
-   * @param {String} tzid     Timezone identifier (e.g. America/Los_Angeles)
-   * @return {?Timezone}      The timezone, or null if not found
+   * @param {String} tzid               Timezone identifier (e.g. America/Los_Angeles)
+   * @return {Timezone | undefined}     The timezone, or undefined if not found
    */
   get: function(tzid) {
     if (zones === null) {