diff --git a/src/auth/server.ts b/src/auth/server.ts
index a33c593..4d7556f 100644
--- a/src/auth/server.ts
+++ b/src/auth/server.ts
@@ -6,13 +6,31 @@ import type { CreateAuthOptions, SessionUser } from "./types";
 
 export type { SessionUser, CreateAuthOptions };
 
+/**
+ * Shape of the GET/POST route handlers NextAuth returns. Declared
+ * structurally (Request → Response) rather than via
+ * `NextAuthResult["handlers"]` — that type embeds `NextRequest` from
+ * the kit's own copy of `next`, which conflicts with the consumer's
+ * `next` and produces a spurious `RouteHandlerConfig` mismatch in
+ * `.next/types/validator.ts` for every app's `[...nextauth]/route.ts`.
+ *
+ * Web-standard `Request`/`Response` are valid for Next.js route
+ * handlers (NextRequest extends Request), and TS function-parameter
+ * contravariance makes this assignable wherever the validator wants
+ * `(request: NextRequest, ctx) => ...`.
+ */
+export type AuthRouteHandlers = {
+  GET: (request: Request) => Promise<Response>;
+  POST: (request: Request) => Promise<Response>;
+};
+
 /**
  * Result of `createAuth()`. Mirrors NextAuth's return value plus
  * `requireAuth` and the resolved `signInPath` so consumers don't have to
  * thread these around.
  */
 export interface AuthBundle {
-  handlers: NextAuthResult["handlers"];
+  handlers: AuthRouteHandlers;
   signIn: NextAuthResult["signIn"];
   signOut: NextAuthResult["signOut"];
   auth: NextAuthResult["auth"];
@@ -114,7 +132,12 @@ export function createAuth(opts: CreateAuthOptions): AuthBundle {
   }
 
   return {
-    handlers: na.handlers,
+    // Cast through unknown: NextAuth's handler param type references its
+    // own NextRequest; the AuthRouteHandlers shape is structurally
+    // compatible (NextRequest extends Request), but TS can't prove the
+    // function-parameter contravariance across the two `next` copies on
+    // its own.
+    handlers: na.handlers as unknown as AuthRouteHandlers,
     signIn: na.signIn,
     signOut: na.signOut,
     auth: na.auth,