diff --git a/.changeset/plain-rockets-grow.md b/.changeset/plain-rockets-grow.md
new file mode 100644
index 00000000..f55e5d2f
--- /dev/null
+++ b/.changeset/plain-rockets-grow.md
@@ -0,0 +1,5 @@
+---
+'@hono/oidc-auth': patch
+---
+
+Add explicit `MiddlewareHandler` return type
diff --git a/packages/oidc-auth/src/index.ts b/packages/oidc-auth/src/index.ts
index 4975a008..17f12e5c 100644
--- a/packages/oidc-auth/src/index.ts
+++ b/packages/oidc-auth/src/index.ts
@@ -2,7 +2,7 @@
  * OpenID Connect authentication middleware for hono
  */
 
-import type { Context, MiddlewareHandler, OidcAuthClaims } from 'hono'
+import type { Context, MiddlewareHandler, OidcAuthClaims, TypedResponse } from 'hono'
 import { env } from 'hono/adapter'
 import { deleteCookie, getCookie, setCookie } from 'hono/cookie'
 import { createMiddleware } from 'hono/factory'
@@ -66,7 +66,7 @@ export type OidcAuthEnv = {
  * If used, should be called before any other OIDC middleware or functions for the Hono context.
  * Unconfigured values will fallback to environment variables.
  */
-export const initOidcAuthMiddleware = (config: Partial<OidcAuthEnv>) => {
+export const initOidcAuthMiddleware = (config: Partial<OidcAuthEnv>): MiddlewareHandler => {
   return createMiddleware(async (c, next) => {
     setOidcAuthEnv(c, config)
     await next()
@@ -356,7 +356,9 @@ const generateAuthorizationRequestUrl = async (
 /**
  * Processes the OAuth2 callback request.
  */
-export const processOAuthCallback = async (c: Context) => {
+export const processOAuthCallback = async (
+  c: Context
+): Promise<Response & TypedResponse<undefined, 302, 'redirect'>> => {
   const env = getOidcAuthEnv(c)
   const as = await getAuthorizationServer(c)
   const client = getClient(c)
diff --git a/packages/oidc-auth/tsconfig.build.json b/packages/oidc-auth/tsconfig.build.json
index ccc2f65a..a82a1266 100644
--- a/packages/oidc-auth/tsconfig.build.json
+++ b/packages/oidc-auth/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"],