diff --git a/src/withESI.test.tsx b/src/withESI.test.tsx
index 875fcbc..385da72 100644
--- a/src/withESI.test.tsx
+++ b/src/withESI.test.tsx
@@ -1,4 +1,3 @@
-import express from "express";
 import React from "react";
 import renderer from "react-test-renderer";
 import withESI from "./withESI";
@@ -9,7 +8,7 @@ test("client-side", () => {
   const DummyESI = withESI(Dummy, "id");
   expect(DummyESI.displayName).toBe("WithESI(Dummy)");
 
-  (global.process as any).browser = true;
+  (global as any).navigator = {};
   const component = renderer.create(<DummyESI name="Kévin" />);
   expect(component).toMatchSnapshot();
 });
@@ -18,7 +17,7 @@ test("client-side with serialized props", () => {
   const DummyESI = withESI(Dummy, "id");
   expect(DummyESI.displayName).toBe("WithESI(Dummy)");
 
-  (global.process as any).browser = true;
+  (global as any).navigator = {};
   ((global as any).__REACT_ESI__ as any) = { id: { name: "Anne" } };
   const component = renderer.create(<DummyESI />);
   expect(component).toMatchSnapshot();
@@ -35,7 +34,7 @@ test("client-side call getInitialProps", async () => {
 
   const ComponentESI = withESI(Component, "initial-props");
 
-  (global.process as any).browser = true;
+  (global as any).navigator = {};
   renderer.create(<ComponentESI />);
   expect(called).toBe(true);
 });
@@ -45,7 +44,7 @@ test("server-side", () => {
   expect(DummyESI.displayName).toBe("WithESI(Dummy)");
 
   process.env.REACT_ESI_SECRET = "dummy";
-  (global.process as any).browser = false;
+  delete (global as any).navigator;
   const component = renderer.create(
     <DummyESI esi={{ attrs: { onerror: "continue" } }} name="Kévin" />
   );
diff --git a/src/withESI.tsx b/src/withESI.tsx
index 22bdae8..7995bfb 100644
--- a/src/withESI.tsx
+++ b/src/withESI.tsx
@@ -8,10 +8,6 @@ declare global {
   }
 }
 
-interface IWebpackProcess extends NodeJS.Process {
-  browser?: boolean;
-}
-
 interface IWithESIProps {
   esi?: {
     attrs?: object;
@@ -46,7 +42,7 @@ export default function withESI<P>(
       this.esi = esi || {};
       this.state.childProps = childProps;
 
-      if (!(process as IWebpackProcess).browser) {
+      if (typeof navigator === 'undefined') {
         return;
       }
 
@@ -81,7 +77,7 @@ export default function withESI<P>(
     }
 
     public render() {
-      if ((process as IWebpackProcess).browser) {
+      if (typeof navigator !== 'undefined') {
         return (
           <div>
             <WrappedComponent {...this.state.childProps as P} />