diff --git a/deno_dist/middleware/etag/index.ts b/deno_dist/middleware/etag/index.ts
index 6c44ae6fd..e14b002ed 100644
--- a/deno_dist/middleware/etag/index.ts
+++ b/deno_dist/middleware/etag/index.ts
@@ -12,7 +12,7 @@ type ETagOptions = {
  * > would have been sent in an equivalent 200 OK response: Cache-Control,
  * > Content-Location, Date, ETag, Expires, and Vary.
  */
-const RETAINED_304_HEADERS = [
+export const RETAINED_304_HEADERS = [
   'cache-control',
   'content-location',
   'date',
diff --git a/src/middleware/etag/index.test.ts b/src/middleware/etag/index.test.ts
index 18d3660c3..d70ce2abc 100644
--- a/src/middleware/etag/index.test.ts
+++ b/src/middleware/etag/index.test.ts
@@ -1,11 +1,9 @@
 import { Hono } from '../../hono'
-import { etag } from '.'
+import { etag, RETAINED_304_HEADERS } from '.'
 
 describe('Etag Middleware', () => {
-  let app: Hono
-
-  beforeEach(() => {
-    app = new Hono()
+  it('Should return etag header', async () => {
+    const app = new Hono()
     app.use('/etag/*', etag())
     app.get('/etag/abc', (c) => {
       return c.text('Hono is cool')
@@ -13,9 +11,6 @@ describe('Etag Middleware', () => {
     app.get('/etag/def', (c) => {
       return c.json({ message: 'Hono is cool' })
     })
-  })
-
-  it('Should return etag header', async () => {
     let res = await app.request('http://localhost/etag/abc')
     expect(res.headers.get('ETag')).not.toBeFalsy()
     expect(res.headers.get('ETag')).toBe('"4e32298b1cb4edc595237405e5b696e105c2399a"')
@@ -26,18 +21,21 @@ describe('Etag Middleware', () => {
   })
 
   it('Should return etag header - binary', async () => {
-    app.use('/etag-binary/*', etag())
-    app.get('/etag-binary', async (c) => {
+    const app = new Hono()
+    app.use('/etag/*', etag())
+    app.get('/etag', async (c) => {
       return c.body(new Uint8Array(1))
     })
 
-    const res = await app.request('http://localhost/etag-binary')
+    const res = await app.request('http://localhost/etag')
     expect(res.headers.get('ETag')).not.toBeFalsy()
     const etagHeader = res.headers.get('ETag')
     expect(etagHeader).toBe('"5ba93c9db0cff93f52b521d7420e43f6eda2784f"')
   })
 
   it('Should not be the same etag - arrayBuffer', async () => {
+    const app = new Hono()
+    app.use('/etag/*', etag())
     app.get('/etag/ab1', (c) => {
       return c.body(new ArrayBuffer(1))
     })
@@ -52,6 +50,8 @@ describe('Etag Middleware', () => {
   })
 
   it('Should not be the same etag - Uint8Array', async () => {
+    const app = new Hono()
+    app.use('/etag/*', etag())
     app.get('/etag/ui1', (c) => {
       return c.body(new Uint8Array([1, 2, 3]))
     })
@@ -66,17 +66,20 @@ describe('Etag Middleware', () => {
   })
 
   it('Should return etag header - weak', async () => {
-    app.use('/etag-weak/*', etag({ weak: true }))
-    app.get('/etag-weak/abc', (c) => {
+    const app = new Hono()
+    app.use('/etag/*', etag({ weak: true }))
+    app.get('/etag/abc', (c) => {
       return c.text('Hono is cool')
     })
 
-    const res = await app.request('http://localhost/etag-weak/abc')
+    const res = await app.request('http://localhost/etag/abc')
     expect(res.headers.get('ETag')).not.toBeFalsy()
     expect(res.headers.get('ETag')).toBe('W/"4e32298b1cb4edc595237405e5b696e105c2399a"')
   })
 
   it('Should handle conditional GETs', async () => {
+    const app = new Hono()
+    app.use('/etag/*', etag())
     app.get('/etag/ghi', (c) =>
       c.text('Hono is great', 200, {
         'cache-control': 'public, max-age=120',
@@ -91,7 +94,7 @@ describe('Etag Middleware', () => {
     let res = await app.request('http://localhost/etag/ghi')
     expect(res.status).toBe(200)
     expect(res.headers.get('ETag')).not.toBeFalsy()
-    const etag = res.headers.get('ETag') || ''
+    const etagHeaderValue = res.headers.get('ETag') || ''
 
     // conditional GET with the wrong ETag:
     res = await app.request('http://localhost/etag/ghi', {
@@ -104,11 +107,11 @@ describe('Etag Middleware', () => {
     // conditional GET with matching ETag:
     res = await app.request('http://localhost/etag/ghi', {
       headers: {
-        'If-None-Match': etag,
+        'If-None-Match': etagHeaderValue,
       },
     })
     expect(res.status).toBe(304)
-    expect(res.headers.get('Etag')).toBe(etag)
+    expect(res.headers.get('Etag')).toBe(etagHeaderValue)
     expect(await res.text()).toBe('')
     expect(res.headers.get('cache-control')).toBe('public, max-age=120')
     expect(res.headers.get('date')).toBe('Mon, Feb 27 2023 12:08:36 GMT')
@@ -119,23 +122,26 @@ describe('Etag Middleware', () => {
     // conditional GET with matching ETag among list:
     res = await app.request('http://localhost/etag/ghi', {
       headers: {
-        'If-None-Match': `"mismatch 1", ${etag}, "mismatch 2"`,
+        'If-None-Match': `"mismatch 1", ${etagHeaderValue}, "mismatch 2"`,
       },
     })
     expect(res.status).toBe(304)
   })
 
   it('Should not return duplicate etag header values', async () => {
-    app.use('/etag2/*', etag())
-    app.use('/etag2/*', etag())
-    app.get('/etag2/abc', (c) => c.text('Hono is cool'))
+    const app = new Hono()
+    app.use('/etag/*', etag())
+    app.use('/etag/*', etag())
+    app.get('/etag/abc', (c) => c.text('Hono is cool'))
 
-    const res = await app.request('http://localhost/etag2/abc')
+    const res = await app.request('http://localhost/etag/abc')
     expect(res.headers.get('ETag')).not.toBeFalsy()
     expect(res.headers.get('ETag')).toBe('"4e32298b1cb4edc595237405e5b696e105c2399a"')
   })
 
   it('Should not override ETag headers from upstream', async () => {
+    const app = new Hono()
+    app.use('/etag/*', etag())
     app.get('/etag/predefined', (c) =>
       c.text('This response has an ETag', 200, { ETag: '"f-0194-d"' })
     )
@@ -143,4 +149,34 @@ describe('Etag Middleware', () => {
     const res = await app.request('http://localhost/etag/predefined')
     expect(res.headers.get('ETag')).toBe('"f-0194-d"')
   })
+
+  it('Should retain the default and the specified headers', async () => {
+    const cacheControl = 'public, max-age=120'
+    const message = 'Hello!'
+    const app = new Hono()
+    app.use(
+      '/etag/*',
+      etag({
+        retainedHeaders: ['x-message-retain', ...RETAINED_304_HEADERS],
+      })
+    )
+    app.get('/etag', (c) => {
+      return c.text('Hono is cool', 200, {
+        'cache-control': cacheControl,
+        'x-message-retain': message,
+        'x-message': message,
+      })
+    })
+    const res = await app.request('/etag', {
+      headers: {
+        'If-None-Match': '"4e32298b1cb4edc595237405e5b696e105c2399a"',
+      },
+    })
+    expect(res.status).toBe(304)
+    expect(res.headers.get('ETag')).not.toBeFalsy()
+    expect(res.headers.get('ETag')).toBe('"4e32298b1cb4edc595237405e5b696e105c2399a"')
+    expect(res.headers.get('Cache-Control')).toBe(cacheControl)
+    expect(res.headers.get('x-message-retain')).toBe(message)
+    expect(res.headers.get('x-message')).toBeFalsy()
+  })
 })
diff --git a/src/middleware/etag/index.ts b/src/middleware/etag/index.ts
index ba3d86c6f..bc25ae041 100644
--- a/src/middleware/etag/index.ts
+++ b/src/middleware/etag/index.ts
@@ -12,7 +12,7 @@ type ETagOptions = {
  * > would have been sent in an equivalent 200 OK response: Cache-Control,
  * > Content-Location, Date, ETag, Expires, and Vary.
  */
-const RETAINED_304_HEADERS = [
+export const RETAINED_304_HEADERS = [
   'cache-control',
   'content-location',
   'date',