diff --git a/packages/ts/frontend/src/Connect.ts b/packages/ts/frontend/src/Connect.ts
index 4b1ae3b282..7369ec04b8 100644
--- a/packages/ts/frontend/src/Connect.ts
+++ b/packages/ts/frontend/src/Connect.ts
@@ -16,7 +16,7 @@ import {
 } from './FluxConnection.js';
 import type { VaadinWindow } from './types.js';
 
-const $wnd = window as VaadinWindow;
+const $wnd = self as VaadinWindow;
 
 $wnd.Vaadin ??= {};
 $wnd.Vaadin.registrations ??= [];
@@ -300,7 +300,8 @@ export class ConnectClient {
       throw new TypeError(`2 arguments required, but got only ${arguments.length}`);
     }
 
-    const csrfHeaders = getCsrfTokenHeadersForEndpointRequest(document);
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+    const csrfHeaders = self.document ? getCsrfTokenHeadersForEndpointRequest(self.document) : {};
     const headers: Record<string, string> = {
       Accept: 'application/json',
       'Content-Type': 'application/json',
diff --git a/packages/ts/frontend/src/CookieManager.ts b/packages/ts/frontend/src/CookieManager.ts
index de4e11cb53..90999e6b69 100644
--- a/packages/ts/frontend/src/CookieManager.ts
+++ b/packages/ts/frontend/src/CookieManager.ts
@@ -5,7 +5,8 @@ export function calculatePath({ pathname }: URL): string {
 }
 
 const CookieManager: Cookies.CookiesStatic = Cookies.withAttributes({
-  path: calculatePath(new URL(document.baseURI)),
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+  path: calculatePath(new URL(self.document?.baseURI ?? '/')),
 });
 
 export default CookieManager;
diff --git a/packages/ts/frontend/src/FluxConnection.ts b/packages/ts/frontend/src/FluxConnection.ts
index 4fef3a3019..562f5594a0 100644
--- a/packages/ts/frontend/src/FluxConnection.ts
+++ b/packages/ts/frontend/src/FluxConnection.ts
@@ -182,7 +182,8 @@ export class FluxConnection extends EventTarget {
   }
 
   #connectWebsocket(prefix: string, atmosphereOptions: Partial<Atmosphere.Request>) {
-    const extraHeaders = getCsrfTokenHeadersForEndpointRequest(document);
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+    const extraHeaders = self.document ? getCsrfTokenHeadersForEndpointRequest(self.document) : {};
     const pushUrl = 'HILLA/push';
     const url = prefix.length === 0 ? pushUrl : (prefix.endsWith('/') ? prefix : `${prefix}/`) + pushUrl;
     this.#socket = atmosphere.subscribe?.({
diff --git a/packages/ts/react-i18n/src/index.ts b/packages/ts/react-i18n/src/index.ts
index 5ef8f73227..a46f7e12e0 100644
--- a/packages/ts/react-i18n/src/index.ts
+++ b/packages/ts/react-i18n/src/index.ts
@@ -31,7 +31,7 @@ export class I18n {
 
   constructor() {
     // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
-    if (!(window as any).Vaadin?.featureFlags?.hillaI18n) {
+    if (!(self as any).Vaadin?.featureFlags?.hillaI18n) {
       // Remove when removing feature flag
       throw new Error(
         `The Hilla I18n API is currently considered experimental and may change in the future. To use it you need to explicitly enable it in Copilot or by adding com.vaadin.experimental.hillaI18n=true to vaadin-featureflags.properties`,
diff --git a/packages/ts/react-signals/src/FullStackSignal.ts b/packages/ts/react-signals/src/FullStackSignal.ts
index 1b96087c8d..58926c971d 100644
--- a/packages/ts/react-signals/src/FullStackSignal.ts
+++ b/packages/ts/react-signals/src/FullStackSignal.ts
@@ -28,7 +28,7 @@ export abstract class DependencyTrackingSignal<T> extends Signal<T> {
 
   protected constructor(value: T | undefined, onFirstSubscribe: () => void, onLastUnsubscribe: () => void) {
     // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
-    if (!(window as any).Vaadin?.featureFlags?.fullstackSignals) {
+    if (!(self as any).Vaadin?.featureFlags?.fullstackSignals) {
       // Remove when removing feature flag
       throw new Error(
         `The Hilla Fullstack Signals API is currently considered experimental and may change in the future. To use it you need to explicitly enable it in Copilot or by adding com.vaadin.experimental.fullstackSignals=true to vaadin-featureflags.properties`,