diff --git a/test/core/test/environments/custom-env.test.ts b/test/core/test/environments/custom-env.test.ts
index cd4ba6a9bef3..e0b8a6d3502a 100644
--- a/test/core/test/environments/custom-env.test.ts
+++ b/test/core/test/environments/custom-env.test.ts
@@ -2,6 +2,11 @@
 
 import { expect, test } from 'vitest'
 
+test('TextDecoder and TextEncoder are available', () => {
+  expect(typeof TextDecoder).toBe('function')
+  expect(typeof TextEncoder).toBe('function')
+})
+
 test('custom env is defined', () => {
   expect(expect.getState().environment).toBe('custom')
   expect((globalThis as any).testEnvironment).toBe('custom')
diff --git a/test/core/vitest-environment-custom/index.ts b/test/core/vitest-environment-custom/index.ts
index f03f22f92de4..72694817b8b7 100644
--- a/test/core/vitest-environment-custom/index.ts
+++ b/test/core/vitest-environment-custom/index.ts
@@ -19,6 +19,8 @@ export default <Environment>{
       AbortController,
       EventTarget,
       Event,
+      TextDecoder,
+      TextEncoder,
     })
     return {
       getVmContext() {