diff --git a/packages/browser/src/integrations/useragent.ts b/packages/browser/src/integrations/useragent.ts
index 925255f074e9..17e06a6789fc 100644
--- a/packages/browser/src/integrations/useragent.ts
+++ b/packages/browser/src/integrations/useragent.ts
@@ -1,5 +1,4 @@
-import { addGlobalEventProcessor, getCurrentHub } from '@sentry/core';
-import { Event, Integration } from '@sentry/types';
+import { Event, EventProcessor, Hub, Integration } from '@sentry/types';
 import { getGlobalObject } from '@sentry/utils';
 
 const global = getGlobalObject<Window>();
@@ -19,25 +18,35 @@ export class UserAgent implements Integration {
   /**
    * @inheritDoc
    */
-  public setupOnce(): void {
+  public setupOnce(addGlobalEventProcessor: (callback: EventProcessor) => void, getCurrentHub: () => Hub): void {
     addGlobalEventProcessor((event: Event) => {
       if (getCurrentHub().getIntegration(UserAgent)) {
+        const { navigator, location, document } = global;
         // if none of the information we want exists, don't bother
-        if (!global.navigator && !global.location && !global.document) {
+        if (!navigator && !location && !document) {
           return event;
         }
 
-        // grab as much info as exists and add it to the event
-        const url = event.request?.url || global.location?.href;
-        const { referrer } = global.document || {};
-        const { userAgent } = global.navigator || {};
-
-        const headers = {
-          ...event.request?.headers,
-          ...(referrer && { Referer: referrer }),
-          ...(userAgent && { 'User-Agent': userAgent }),
-        };
-        const request = { ...(url && { url }), headers };
+        const req = event.request;
+        const headers = req && req.headers ? { ...req.headers } : {};
+
+        const { userAgent } = navigator || {};
+        if (userAgent) {
+          headers['User-Agent'] = userAgent;
+        }
+
+        const { referrer } = document || {};
+        if (referrer) {
+          headers.Referer = referrer;
+        }
+
+        const request = { headers } as Record<string, unknown>;
+
+        const { href } = location || {};
+        const url = (req && req.url) || href;
+        if (url) {
+          request.url = url;
+        }
 
         return { ...event, request };
       }