diff --git a/packages/vitest/src/node/printError.ts b/packages/vitest/src/node/printError.ts
index 45c87f9e9..2a7bedf6b 100644
--- a/packages/vitest/src/node/printError.ts
+++ b/packages/vitest/src/node/printError.ts
@@ -243,9 +243,19 @@ function printErrorInner(
     )
   }
 
-  if (typeof e.cause === 'object' && e.cause && 'name' in e.cause) {
-    (e.cause as any).name = `Caused by: ${(e.cause as any).name}`
-    printErrorInner(e.cause, project, {
+  if (e.cause != null) {
+    let cause: any = e.cause
+    if (typeof cause !== 'object' || cause === null) {
+      const causeStr = String(cause)
+      cause = { name: 'Caused by', message: causeStr, stack: causeStr }
+    }
+    else if (!('name' in cause)) {
+      cause = { ...cause, name: 'Caused by' }
+    }
+    else {
+      cause.name = `Caused by: ${cause.name}`
+    }
+    printErrorInner(cause, project, {
       showCodeFrame: false,
       logger: options.logger,
       parseErrorStacktrace: options.parseErrorStacktrace,
diff --git a/test/e2e/test/env-setup-non-error-cause.test.ts b/test/e2e/test/env-setup-non-error-cause.test.ts
new file mode 100644
index 000000000..a324ab2fb
--- /dev/null
+++ b/test/e2e/test/env-setup-non-error-cause.test.ts
@@ -0,0 +1,90 @@
+import { expect, test } from 'vitest'
+import { runInlineTests } from '../../test-utils'
+
+test('non-Error string thrown from env setup surfaces in stderr', async () => {
+  const { stderr } = await runInlineTests({
+    'throwing-env.js': `
+export default {
+  name: 'throwing-env',
+  transformMode: 'ssr',
+  async setup() {
+    throw 'the real reason setup failed (a non-Error value)'
+  },
+}
+    `,
+    'vitest.config.js': `
+import { defineConfig } from 'vitest/config'
+export default defineConfig({
+  test: {
+    environment: './throwing-env.js',
+  },
+})
+    `,
+    'example.test.js': `
+import { test, expect } from 'vitest'
+test('noop', () => { expect(1).toBe(1) })
+    `,
+  })
+
+  expect(stderr).toContain('Failed to start')
+  expect(stderr).toContain('the real reason setup failed (a non-Error value)')
+})
+
+test('non-Error plain object thrown from env setup surfaces in stderr', async () => {
+  const { stderr } = await runInlineTests({
+    'throwing-env.js': `
+export default {
+  name: 'throwing-env',
+  transformMode: 'ssr',
+  async setup() {
+    throw { reason: 'wasm-init-failed', code: 42 }
+  },
+}
+    `,
+    'vitest.config.js': `
+import { defineConfig } from 'vitest/config'
+export default defineConfig({
+  test: {
+    environment: './throwing-env.js',
+  },
+})
+    `,
+    'example.test.js': `
+import { test, expect } from 'vitest'
+test('noop', () => { expect(1).toBe(1) })
+    `,
+  })
+
+  expect(stderr).toContain('Failed to start')
+  expect(stderr).toMatch(/wasm-init-failed|reason/)
+})
+
+test('Error thrown from env setup still renders with Caused by prefix', async () => {
+  const { stderr } = await runInlineTests({
+    'throwing-env.js': `
+export default {
+  name: 'throwing-env',
+  transformMode: 'ssr',
+  async setup() {
+    throw new Error('explicit error reason')
+  },
+}
+    `,
+    'vitest.config.js': `
+import { defineConfig } from 'vitest/config'
+export default defineConfig({
+  test: {
+    environment: './throwing-env.js',
+  },
+})
+    `,
+    'example.test.js': `
+import { test, expect } from 'vitest'
+test('noop', () => { expect(1).toBe(1) })
+    `,
+  })
+
+  expect(stderr).toContain('Failed to start')
+  expect(stderr).toContain('Caused by')
+  expect(stderr).toContain('explicit error reason')
+})
diff --git a/test/e2e/test/stacktraces.test.ts b/test/e2e/test/stacktraces.test.ts
index 4bdcd8396..4b3ecc690 100644
--- a/test/e2e/test/stacktraces.test.ts
+++ b/test/e2e/test/stacktraces.test.ts
@@ -292,6 +292,7 @@ it('resolves/rejects', async () => {
            18|       })
            19|
 
+      Caused by: 3
       ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯[4/4]⎯
 
       "
@@ -371,6 +372,7 @@ it('resolves/rejects', async () => {
          18|       })
          19|
 
+    Caused by: 3
     ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯[4/4]⎯
 
     "