diff --git a/CHANGELOG.md b/CHANGELOG.md
index eb6d437..bfac944 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 4.0.1 (July 25th, 2019)
+
+* Forgot to update MJS file.
+
 ## 4.0.0 (July 25th, 2019)
 
 * Custom data support for FullStory - [dtsellos03](https://github.com/dtsellos03)
diff --git a/src/wildberry-princess.mjs b/src/wildberry-princess.mjs
index 50f2fc6..2f917f2 100644
--- a/src/wildberry-princess.mjs
+++ b/src/wildberry-princess.mjs
@@ -152,10 +152,11 @@ export default class WildberryPrincess {
     // http://help.fullstory.com/develop-js/setuservars
     // Pass in customFields if provided - must be in the FullStory userVars format - see above
     if (this.settings.useFullStory && window.FS != null && user.id !== 'anonymous') {
+      const customFields = user.customFields ? user.customFields : {};
       window.FS.identify(user.id, {
         displayName: user.name,
         email: user.email,
-        ...user.customFields,
+        ...customFields,
       });
     }