diff --git a/packages/dev-test/src/env/browser.spec.ts b/packages/dev-test/src/env/browser.spec.ts
index e38c910..30fa22b 100644
--- a/packages/dev-test/src/env/browser.spec.ts
+++ b/packages/dev-test/src/env/browser.spec.ts
@@ -23,4 +23,9 @@ describe('browser', () => {
   it('contains HTML*Element', () => {
     expect(typeof all.HTMLElement).toBe('function');
   });
+
+  it('dispatches the global CustomEvent and Event on window', () => {
+    expect(() => window.dispatchEvent(new CustomEvent('custom', { detail: 1 }))).not.toThrow();
+    expect(() => window.dispatchEvent(new Event('plain'))).not.toThrow();
+  });
 });
diff --git a/packages/dev-test/src/env/browser.ts b/packages/dev-test/src/env/browser.ts
index 39377a1..0a702a0 100644
--- a/packages/dev-test/src/env/browser.ts
+++ b/packages/dev-test/src/env/browser.ts
@@ -3,6 +3,13 @@
 
 import { JSDOM } from 'jsdom';
 
+/**
+ * Constructors that Node defines as well. A DOM node only accepts an event
+ * created in its own realm, so in the browser environment the JSDOM ones
+ * replace Node's, as they do under jest-environment-jsdom.
+ */
+export const BROWSER_OVERRIDES: readonly string[] = ['CustomEvent', 'Event'];
+
 /**
  * Export a very basic JSDom environment - this is just enough so we have
  * @testing-environment/react tests passing in this repo
@@ -15,6 +22,9 @@ export function browser () {
   const { window } = new JSDOM('', { url: 'http://localhost' });
 
   return {
+    // Event constructors, see BROWSER_OVERRIDES
+    CustomEvent: window.CustomEvent,
+    Event: window.Event,
     // All HTML Elements that are defined on the JSDOM window object.
     // (we copied as-is from the types definition). We cannot get this
     // via Object.keys(window).filter(...) so we have to specify explicitly
diff --git a/packages/dev-test/src/env/index.ts b/packages/dev-test/src/env/index.ts
index 37ce94e..8ec9132 100644
--- a/packages/dev-test/src/env/index.ts
+++ b/packages/dev-test/src/env/index.ts
@@ -1,7 +1,7 @@
 // Copyright 2017-2026 @pezkuwi/dev-test authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
-import { browser } from './browser.js';
+import { browser, BROWSER_OVERRIDES } from './browser.js';
 import { expect } from './expect.js';
 import { jest } from './jest.js';
 import { lifecycle } from './lifecycle.js';
@@ -15,7 +15,11 @@ export function exposeEnv (isBrowser: boolean): void {
     env && Object
       .entries(env())
       .forEach(([key, fn]) => {
-        globalThis[key as 'undefined'] ??= fn;
+        if (isBrowser && BROWSER_OVERRIDES.includes(key)) {
+          (globalThis as Record<string, unknown>)[key] = fn;
+        } else {
+          globalThis[key as 'undefined'] ??= fn;
+        }
       });
   });
 }