diff --git a/src/context.ts b/src/context.ts
index bb9029ca0..e3dbc3c5c 100644
--- a/src/context.ts
+++ b/src/context.ts
@@ -18,8 +18,12 @@ import type {
   JSONValue,
   SimplifyDeepArray,
 } from './utils/types'
+import type { BaseMime } from './utils/mime'
 
-type HeaderRecord = Record<ResponseHeader, string | string[]> | Record<string, string | string[]>
+type HeaderRecord =
+  | Record<'Content-Type', BaseMime>
+  | Record<ResponseHeader, string | string[]>
+  | Record<string, string | string[]>
 
 /**
  * Data type can be a string, ArrayBuffer, or ReadableStream.
@@ -304,14 +308,16 @@ type ResponseHeader =
   | 'X-XSS-Protection'
 
 interface SetHeaders {
+  (name: 'Content-Type', value?: BaseMime, options?: SetHeadersOptions): void
   (name: ResponseHeader, value?: string, options?: SetHeadersOptions): void
   (name: string, value?: string, options?: SetHeadersOptions): void
 }
 
 type ResponseHeadersInit =
   | [string, string][]
-  | Record<string, string>
+  | Record<'Content-Type', BaseMime>
   | Record<ResponseHeader, string>
+  | Record<string, string>
   | Headers
 
 interface ResponseInit {
diff --git a/src/utils/mime.ts b/src/utils/mime.ts
index 26b481aba..afef10487 100644
--- a/src/utils/mime.ts
+++ b/src/utils/mime.ts
@@ -3,7 +3,10 @@
  * MIME utility.
  */
 
-export const getMimeType = (filename: string, mimes = baseMimes): string | undefined => {
+export const getMimeType = (
+  filename: string,
+  mimes: Record<string, string> = baseMimes
+): string | undefined => {
   const regexp = /\.([a-zA-Z0-9]+?)$/
   const match = filename.match(regexp)
   if (!match) {
@@ -25,7 +28,62 @@ export const getExtension = (mimeType: string): string | undefined => {
 }
 
 export { baseMimes as mimes }
-const baseMimes: Record<string, string> = {
+
+/**
+ * Union types for BaseMime
+ */
+export type BaseMime =
+  | 'audio/aac'
+  | 'video/x-msvideo'
+  | 'image/avif'
+  | 'video/av1'
+  | 'application/octet-stream'
+  | 'image/bmp'
+  | 'text/css'
+  | 'text/csv'
+  | 'application/vnd.ms-fontobject'
+  | 'application/epub+zip'
+  | 'image/gif'
+  | 'application/gzip'
+  | 'text/html'
+  | 'image/x-icon'
+  | 'text/calendar'
+  | 'image/jpeg'
+  | 'text/javascript'
+  | 'application/json'
+  | 'application/ld+json'
+  | 'audio/x-midi'
+  | 'audio/mpeg'
+  | 'video/mp4'
+  | 'video/mpeg'
+  | 'audio/ogg'
+  | 'video/ogg'
+  | 'application/ogg'
+  | 'audio/opus'
+  | 'font/otf'
+  | 'application/pdf'
+  | 'image/png'
+  | 'application/rtf'
+  | 'image/svg+xml'
+  | 'image/tiff'
+  | 'video/mp2t'
+  | 'font/ttf'
+  | 'text/plain'
+  | 'application/wasm'
+  | 'video/webm'
+  | 'audio/webm'
+  | 'image/webp'
+  | 'font/woff'
+  | 'font/woff2'
+  | 'application/xhtml+xml'
+  | 'application/xml'
+  | 'application/zip'
+  | 'video/3gpp'
+  | 'video/3gpp2'
+  | 'model/gltf+json'
+  | 'model/gltf-binary'
+
+const baseMimes: Record<string, BaseMime> = {
   aac: 'audio/aac',
   avi: 'video/x-msvideo',
   avif: 'image/avif',