diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1188bdd7..3dee3c41 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 1.4.28 - 3 Mar 2026
+Bug fix:
+- conditional set headers of String and Object when no set.headers is set
+
 # 1.4.27 - 1 Mar 2026
 Bug fix:
 - getSchemaValidator: handle TypeBox as sub type
diff --git a/example/a.ts b/example/a.ts
index 07958600..5bddd460 100644
--- a/example/a.ts
+++ b/example/a.ts
@@ -1,3 +1,22 @@
 import { Elysia } from '../src'
+import { mapEarlyResponse } from '../src/adapter/web-standard/handler'
 
-new Elysia().get('/', 'Hi').listen(3000)
+const body = {
+	name: 'Shiroko'
+}
+
+const context = {
+	headers: {
+		'x-powered-by': 'Elysia',
+		'coffee-scheme': 'Coffee'
+	},
+	status: 418,
+	cookie: {}
+}
+
+const response = await mapEarlyResponse(
+	new Promise((resolve) => resolve(body)),
+	context
+)
+
+console.log(response?.headers)
diff --git a/src/adapter/web-standard/handler.ts b/src/adapter/web-standard/handler.ts
index a679eb34..9dc90ed3 100644
--- a/src/adapter/web-standard/handler.ts
+++ b/src/adapter/web-standard/handler.ts
@@ -58,12 +58,16 @@ export const mapResponse = (
 
 		switch (response?.constructor?.name) {
 			case 'String':
-				set.headers['content-type'] = 'text/plain'
+				if (!set.headers['content-type'])
+					set.headers['content-type'] = 'text/plain'
+
 				return new Response(response as string, set as any)
 
 			case 'Array':
 			case 'Object':
-				set.headers['content-type'] = 'application/json'
+				if (!set.headers['content-type'])
+					set.headers['content-type'] = 'application/json'
+
 				return new Response(JSON.stringify(response), set as any)
 
 			case 'ElysiaFile':
@@ -208,12 +212,16 @@ export const mapEarlyResponse = (
 
 		switch (response?.constructor?.name) {
 			case 'String':
-				set.headers['content-type'] = 'text/plain'
+				if (!set.headers['content-type'])
+					set.headers['content-type'] = 'text/plain'
+
 				return new Response(response as string, set as any)
 
 			case 'Array':
 			case 'Object':
-				set.headers['content-type'] = 'application/json'
+				if (!set.headers['content-type'])
+					set.headers['content-type'] = 'application/json'
+
 				return new Response(JSON.stringify(response), set as any)
 
 			case 'ElysiaFile':
@@ -335,12 +343,16 @@ export const mapEarlyResponse = (
 	} else
 		switch (response?.constructor?.name) {
 			case 'String':
-				set.headers['content-type'] = 'text/plain'
+				if (!set.headers['content-type'])
+					set.headers['content-type'] = 'text/plain'
+
 				return new Response(response as string)
 
 			case 'Array':
 			case 'Object':
-				set.headers['content-type'] = 'application/json'
+				if (!set.headers['content-type'])
+					set.headers['content-type'] = 'application/json'
+
 				return new Response(JSON.stringify(response), set as any)
 
 			case 'ElysiaFile':
diff --git a/test/adapter/web-standard/map-early-response.test.ts b/test/adapter/web-standard/map-early-response.test.ts
index 527a9cc5..ae99c826 100644
--- a/test/adapter/web-standard/map-early-response.test.ts
+++ b/test/adapter/web-standard/map-early-response.test.ts
@@ -10,14 +10,14 @@ const defaultContext = {
 	cookie: {}
 }
 
-const context = {
+const createContext = () => ({
 	headers: {
 		'x-powered-by': 'Elysia',
 		'coffee-scheme': 'Coffee'
 	},
 	status: 418,
 	cookie: {}
-}
+})
 
 class Student {
 	constructor(public name: string) {}
@@ -160,6 +160,7 @@ describe('Web Standard - Map Early Response', () => {
 	})
 
 	it('map primitive with custom context', async () => {
+		const context = createContext()
 		const response = mapEarlyResponse('Shiroko', context)
 
 		expect(response).toBeInstanceOf(Response)
@@ -169,6 +170,7 @@ describe('Web Standard - Map Early Response', () => {
 	})
 
 	it('map Function with custom context', async () => {
+		const context = createContext()
 		const response = await mapEarlyResponse(() => 1, context)
 
 		expect(response).toBeInstanceOf(Response)
@@ -180,6 +182,8 @@ describe('Web Standard - Map Early Response', () => {
 	})
 
 	it('map Promise with custom context', async () => {
+		const context = createContext()
+
 		const body = {
 			name: 'Shiroko'
 		}
@@ -199,6 +203,7 @@ describe('Web Standard - Map Early Response', () => {
 	})
 
 	it('map Error with custom context', async () => {
+		const context = createContext()
 		const response = mapEarlyResponse(new Error('Hello'), context)
 
 		expect(response).toBeInstanceOf(Response)
@@ -211,6 +216,7 @@ describe('Web Standard - Map Early Response', () => {
 	})
 
 	it('map Response with custom context', async () => {
+		const context = createContext()
 		const response = await mapEarlyResponse(
 			new Response('Shiroko'),
 			context
@@ -223,6 +229,8 @@ describe('Web Standard - Map Early Response', () => {
 	})
 
 	it('map Response and merge Headers', async () => {
+		const context = createContext()
+
 		const response = await mapEarlyResponse(
 			new Response('Shiroko', {
 				headers: {
diff --git a/test/adapter/web-standard/map-response.test.ts b/test/adapter/web-standard/map-response.test.ts
index ae827fc7..cc5cbc53 100644
--- a/test/adapter/web-standard/map-response.test.ts
+++ b/test/adapter/web-standard/map-response.test.ts
@@ -12,15 +12,6 @@ const createContext = () => ({
 	status: 200
 })
 
-const context = {
-	cookie: {},
-	headers: {
-		'x-powered-by': 'Elysia',
-		'coffee-scheme': 'Coffee'
-	},
-	status: 418
-}
-
 class Student {
 	constructor(public name: string) {}
 
@@ -186,33 +177,37 @@ describe('Web Standard - Map Response', () => {
 	})
 
 	it('map primitive with custom context', async () => {
+		const context = createContext()
 		const response = mapResponse('Shiroko', context)
 
 		expect(response).toBeInstanceOf(Response)
 		expect(await response.text()).toBe('Shiroko')
 		expect(response.headers.toJSON()).toEqual(context.headers)
-		expect(response.status).toBe(418)
+		expect(response.status).toBe(200)
 	})
 
 	it('map undefined with context', async () => {
+		const context = createContext()
 		const response = mapResponse(undefined, context)
 
 		expect(response).toBeInstanceOf(Response)
 		expect(await response.text()).toEqual('')
 		expect(response.headers.toJSON()).toEqual(context.headers)
-		expect(response.status).toBe(418)
+		expect(response.status).toBe(200)
 	})
 
 	it('map null with custom context', async () => {
+		const context = createContext()
 		const response = mapResponse(null, context)
 
 		expect(response).toBeInstanceOf(Response)
 		expect(await response.text()).toEqual('')
 		expect(response.headers.toJSON()).toEqual(context.headers)
-		expect(response.status).toBe(418)
+		expect(response.status).toBe(200)
 	})
 
 	it('map Function with custom context', async () => {
+		const context = createContext()
 		const response = await mapResponse(() => 1, context)
 
 		expect(response).toBeInstanceOf(Response)
@@ -220,10 +215,12 @@ describe('Web Standard - Map Response', () => {
 		expect(response.headers.toJSON()).toEqual({
 			...context.headers
 		})
-		expect(response.status).toBe(418)
+		expect(response.status).toBe(200)
 	})
 
 	it('map Promise with custom context', async () => {
+		const context = createContext()
+
 		const body = {
 			name: 'Shiroko'
 		}
@@ -239,10 +236,12 @@ describe('Web Standard - Map Response', () => {
 			...context.headers,
 			'content-type': 'application/json'
 		})
-		expect(response.status).toBe(418)
+		expect(response.status).toBe(200)
 	})
 
 	it('map Error with custom context', async () => {
+		const context = createContext()
+
 		const response = mapResponse(new Error('Hello'), context)
 
 		expect(response).toBeInstanceOf(Response)
@@ -251,10 +250,12 @@ describe('Web Standard - Map Response', () => {
 			message: 'Hello'
 		})
 		expect(response.headers.toJSON()).toEqual(context.headers)
-		expect(response.status).toBe(418)
+		expect(response.status).toBe(500)
 	})
 
 	it('map Response with custom context', async () => {
+		const context = createContext()
+
 		const response = await mapResponse(new Response('Shiroko'), context)
 		const headers = response.headers.toJSON()
 
@@ -264,6 +265,8 @@ describe('Web Standard - Map Response', () => {
 	})
 
 	it('map Response and merge Headers', async () => {
+		const context = createContext()
+
 		const response = await mapResponse(
 			new Response('Shiroko', {
 				headers: {
@@ -438,4 +441,20 @@ describe('Web Standard - Map Response', () => {
 
 		expect(response).toBe('b')
 	})
+
+	it('respect set.headers on string response', async () => {
+		const app = new Elysia()
+			.onAfterHandle(({ set }) => {
+				set.headers['content-type'] = 'text/html; charset=utf8'
+
+				return '<h1>Hina</h1>'
+			})
+			.get('/', () => 'a')
+
+		const response = await app.handle(req('/'))
+
+		expect(response.headers.get('content-type')).toBe(
+			'text/html; charset=utf8'
+		)
+	})
 })
diff --git a/test/core/native-static.test.ts b/test/core/native-static.test.ts
index 227f121a..b6b5a12b 100644
--- a/test/core/native-static.test.ts
+++ b/test/core/native-static.test.ts
@@ -31,17 +31,11 @@ describe('Native Static Response', () => {
 			.get('/', 'Static Content')
 
 		expect(app.router.response['/'].GET).toBeInstanceOf(Response)
-		expect(app.router.response['/'].GET.headers.toJSON()).toEqual({
-			'content-type': 'text/plain',
-			server: 'Elysia'
-		})
+		expect(app.router.response['/'].GET.headers.get('server')).toBe('Elysia')
 		expect(await app.router.response['/'].GET.text()).toEqual('Static Content')
 
 		expect(app.router.response['/plugin'].GET).toBeInstanceOf(Response)
-		expect(app.router.response['/plugin'].GET.headers.toJSON()).toEqual({
-			'content-type': 'text/plain',
-			server: 'Elysia'
-		})
+		expect(app.router.response['/plugin'].GET.headers.get('server')).toBe('Elysia')
 		expect(await app.router.response['/plugin'].GET.text()).toEqual('Plugin')
 	})