diff --git a/.changeset/tangy-forks-travel.md b/.changeset/tangy-forks-travel.md
new file mode 100644
index 00000000..a49ac5df
--- /dev/null
+++ b/.changeset/tangy-forks-travel.md
@@ -0,0 +1,5 @@
+---
+'@hono/esbuild-transpiler': patch
+---
+
+Add explicit `MiddlewareHandler` return type
diff --git a/packages/esbuild-transpiler/src/transpiler.ts b/packages/esbuild-transpiler/src/transpiler.ts
index 6f289a5c..05d720c5 100644
--- a/packages/esbuild-transpiler/src/transpiler.ts
+++ b/packages/esbuild-transpiler/src/transpiler.ts
@@ -1,3 +1,4 @@
+import type { MiddlewareHandler } from 'hono'
 import { createMiddleware } from 'hono/factory'
 import type { transform, initialize } from './types.esbuild'
 
@@ -16,7 +17,7 @@ export type EsbuildTranspilerOptions = {
   transformOptions?: TransformOptions
 }
 
-export const esbuildTranspiler = (options?: EsbuildTranspilerOptions) => {
+export const esbuildTranspiler = (options?: EsbuildTranspilerOptions): MiddlewareHandler => {
   const esbuild: EsbuildLike | undefined = options?.esbuild
 
   return createMiddleware(async (c, next) => {
diff --git a/packages/esbuild-transpiler/src/transpilers/node.ts b/packages/esbuild-transpiler/src/transpilers/node.ts
index 782c4fe7..63e0f0af 100644
--- a/packages/esbuild-transpiler/src/transpilers/node.ts
+++ b/packages/esbuild-transpiler/src/transpilers/node.ts
@@ -1,9 +1,12 @@
 import * as esbuild from 'esbuild'
+import type { MiddlewareHandler } from 'hono'
 import { createMiddleware } from 'hono/factory'
 import { esbuildTranspiler as baseTranspiler } from '../transpiler'
 import type { EsbuildTranspilerOptions } from '../transpiler'
 
-const transpiler = (options?: Partial<Omit<EsbuildTranspilerOptions, 'esbuild'>>) => {
+const transpiler = (
+  options?: Partial<Omit<EsbuildTranspilerOptions, 'esbuild'>>
+): MiddlewareHandler => {
   return createMiddleware(async (c, next) => {
     return await baseTranspiler({
       esbuild,
diff --git a/packages/esbuild-transpiler/src/transpilers/wasm.ts b/packages/esbuild-transpiler/src/transpilers/wasm.ts
index 6688133a..7c5f181e 100644
--- a/packages/esbuild-transpiler/src/transpilers/wasm.ts
+++ b/packages/esbuild-transpiler/src/transpilers/wasm.ts
@@ -1,4 +1,5 @@
 import * as esbuild from 'esbuild-wasm'
+import type { MiddlewareHandler } from 'hono'
 import { createMiddleware } from 'hono/factory'
 import { esbuildTranspiler as baseTranspiler } from '../transpiler'
 import type { EsbuildTranspilerOptions } from '../transpiler'
@@ -10,7 +11,7 @@ const transpiler = (
     wasmModule?: WebAssembly.Module
     wasmURL?: string | URL
   }
-) => {
+): MiddlewareHandler => {
   return createMiddleware(async (c, next) => {
     if (!initialized) {
       if (options.wasmModule) {
diff --git a/packages/esbuild-transpiler/tsconfig.build.json b/packages/esbuild-transpiler/tsconfig.build.json
index ccc2f65a..a82a1266 100644
--- a/packages/esbuild-transpiler/tsconfig.build.json
+++ b/packages/esbuild-transpiler/tsconfig.build.json
@@ -4,7 +4,8 @@
     "rootDir": "src",
     "outDir": "dist",
     "tsBuildInfoFile": "dist/tsconfig.build.tsbuildinfo",
-    "emitDeclarationOnly": false
+    "emitDeclarationOnly": false,
+    "isolatedDeclarations": true
   },
   "include": ["src/**/*.ts"],
   "exclude": ["**/*.test.ts"],