diff --git a/.changeset/light-lamps-chew.md b/.changeset/light-lamps-chew.md
new file mode 100644
index 0000000..5481a1c
--- /dev/null
+++ b/.changeset/light-lamps-chew.md
@@ -0,0 +1,5 @@
+---
+'openapi-fetch': patch
+---
+
+Fix TypeScript lib error, simplify generated types
diff --git a/schema.ts b/schema.ts
new file mode 100644
index 0000000..e69de29
diff --git a/src/index.ts b/src/index.ts
index 210ffba..c16da2b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -13,8 +13,22 @@ export interface BaseParams {
   query?: Record<string, unknown>;
 }
 
-export const methods = ['get', 'put', 'post', 'delete', 'options', 'head', 'patch', 'trace'] as const;
-export type Method = (typeof methods)[number];
+export type Method = 'get' | 'put' | 'post' | 'delete' | 'options' | 'head' | 'patch' | 'trace';
+
+/** Gets a union of paths which have method */
+type PathsWith<T, M extends Method> = {
+  [Path in keyof T]: T[Path] extends { [K in M]: unknown } ? Path : never;
+}[keyof T];
+
+type PathParams<T> = T extends { parameters: any } ? { params: T['parameters'] } : { params?: BaseParams };
+type MethodParams<T> = T extends {
+  parameters: any;
+}
+  ? { params: T['parameters'] }
+  : { params?: BaseParams };
+type Params<T> = PathParams<T> & MethodParams<T>;
+type RequestBody<T> = T extends { requestBody: any } ? { body: Unwrap<T['requestBody']> } : { body?: never };
+type FetchOptions<T> = Params<T> & RequestBody<T> & Omit<RequestInit, 'body'>;
 
 type TruncatedResponse = Omit<Response, 'arrayBuffer' | 'blob' | 'body' | 'clone' | 'formData' | 'json' | 'text'>;
 /** Infer request/response from content type */
@@ -28,90 +42,77 @@ type Unwrap<T> = T extends {
   ? T['content']['*/*']
   : T;
 
-export default function createClient<T>(defaultOptions?: ClientOptions) {
+type Success<T> = T extends { 200: any } ? T[200] : T extends { 201: any } ? T[201] : T extends { 202: any } ? T[202] : T extends { default: any } ? T['default'] : unknown;
+type Error<T> = T extends { 500: any }
+  ? T[500]
+  : T extends { 404: any }
+  ? T[404]
+  : T extends { 402: any }
+  ? T[402]
+  : T extends { 401: any }
+  ? T[401]
+  : T extends { 400: any }
+  ? T[400]
+  : T extends { 422: any }
+  ? T[422]
+  : T extends { 418: any }
+  ? T[418]
+  : T extends { 417: any }
+  ? T[417]
+  : T extends { 416: any }
+  ? T[416]
+  : T extends { 415: any }
+  ? T[415]
+  : T extends { 414: any }
+  ? T[414]
+  : T extends { 413: any }
+  ? T[413]
+  : T extends { 412: any }
+  ? T[412]
+  : T extends { 411: any }
+  ? T[411]
+  : T extends { 410: any }
+  ? T[410]
+  : T extends { 409: any }
+  ? T[409]
+  : T extends { 408: any }
+  ? T[408]
+  : T extends { 407: any }
+  ? T[407]
+  : T extends { 406: any }
+  ? T[406]
+  : T extends { 405: any }
+  ? T[405]
+  : T extends { default: any }
+  ? T['default']
+  : unknown;
+type FetchResponse<T> =
+  | {
+      data: T extends { responses: any } ? NonNullable<Unwrap<Success<T['responses']>>> : unknown;
+      error?: never;
+      response: TruncatedResponse;
+    }
+  | {
+      data?: never;
+      error: T extends { responses: any } ? NonNullable<Unwrap<Error<T['responses']>>> : unknown;
+      response: TruncatedResponse;
+    };
+
+export default function createClient<T>(options?: ClientOptions) {
   const defaultHeaders = new Headers({
     ...DEFAULT_HEADERS,
-    ...(defaultOptions?.headers ?? {}),
+    ...(options?.headers ?? {}),
   });
 
-  /** Gets a union of paths which have method */
-  type PathsWith<M extends Method> = {
-    [Path in keyof T]: T[Path] extends { [K in M]: unknown } ? Path : never;
-  }[keyof T];
+  async function coreFetch<U extends keyof T, M extends keyof T[U]>(url: U, fetchOptions: FetchOptions<T[U][M]>): Promise<FetchResponse<T[U][M]>> {
+    let { headers, body, params = {}, ...init } = fetchOptions || {};
 
-  type FetchResponse<T> =
-    | {
-        data: T extends { responses: any } ? NonNullable<Unwrap<Success<T['responses']>>> : unknown;
-        error?: never;
-        response: TruncatedResponse;
-      }
-    | {
-        data?: never;
-        error: T extends { responses: any } ? NonNullable<Unwrap<Error<T['responses']>>> : unknown;
-        response: TruncatedResponse;
-      };
-
-  type PathParams<T> = T extends { parameters: any } ? { params: T['parameters'] } : { params?: BaseParams };
-  type MethodParams<T> = T extends {
-    parameters: any;
-  }
-    ? { params: T['parameters'] }
-    : { params?: BaseParams };
-  type Params<T> = PathParams<T> & MethodParams<T>;
-  type RequestBody<T> = T extends { requestBody: any } ? { body: Unwrap<T['requestBody']> } : { body?: never };
-  type FetchOptions<T> = Params<T> & RequestBody<T> & Omit<RequestInit, 'body'>;
-  type Success<T> = T extends { 200: any } ? T[200] : T extends { 201: any } ? T[201] : T extends { 202: any } ? T[202] : T extends { default: any } ? T['default'] : unknown;
-  type Error<T> = T extends { 500: any }
-    ? T[500]
-    : T extends { 404: any }
-    ? T[404]
-    : T extends { 402: any }
-    ? T[402]
-    : T extends { 401: any }
-    ? T[401]
-    : T extends { 400: any }
-    ? T[400]
-    : T extends { 422: any }
-    ? T[422]
-    : T extends { 418: any }
-    ? T[418]
-    : T extends { 417: any }
-    ? T[417]
-    : T extends { 416: any }
-    ? T[416]
-    : T extends { 415: any }
-    ? T[415]
-    : T extends { 414: any }
-    ? T[414]
-    : T extends { 413: any }
-    ? T[413]
-    : T extends { 412: any }
-    ? T[412]
-    : T extends { 411: any }
-    ? T[411]
-    : T extends { 410: any }
-    ? T[410]
-    : T extends { 409: any }
-    ? T[409]
-    : T extends { 408: any }
-    ? T[408]
-    : T extends { 407: any }
-    ? T[407]
-    : T extends { 406: any }
-    ? T[406]
-    : T extends { 405: any }
-    ? T[405]
-    : T extends { default: any }
-    ? T['default']
-    : unknown;
-
-  async function coreFetch<U extends keyof T, M extends keyof T[U]>(url: U, options: FetchOptions<T[U][M]>): Promise<FetchResponse<T[U][M]>> {
-    let { headers, body, params = {}, ...init } = options || {};
     // URL
-    let finalURL = `${defaultOptions?.baseUrl ?? ''}${url as string}`;
+    let finalURL = `${options?.baseUrl ?? ''}${url as string}`;
     const { path, query } = (params as BaseParams | undefined) ?? {};
     if (path) for (const [k, v] of Object.entries(path)) finalURL = finalURL.replace(`{${k}}`, encodeURIComponent(`${v}`.trim()));
     if (query) finalURL = `${finalURL}?${new URLSearchParams(query as any).toString()}`;
+
     // headers
     const baseHeaders = new Headers(defaultHeaders); // clone defaults (don’t overwrite!)
     const headerOverrides = new Headers(headers);
@@ -119,10 +120,11 @@ export default function createClient<T>(defaultOptions?: ClientOptions) {
       if (v === undefined || v === null) baseHeaders.delete(k); // allow `undefined` | `null` to erase value
       else baseHeaders.set(k, v);
     }
+
     // fetch!
     const res = await fetch(finalURL, {
       redirect: 'follow',
-      ...defaultOptions,
+      ...options,
       ...init,
       headers: baseHeaders,
       body: typeof body === 'string' ? body : JSON.stringify(body),
@@ -142,36 +144,36 @@ export default function createClient<T>(defaultOptions?: ClientOptions) {
 
   return {
     /** Call a GET endpoint */
-    async get<U extends PathsWith<'get'>, M extends keyof T[U]>(url: U, options: FetchOptions<T[U][M]>) {
-      return coreFetch(url, { ...options, method: 'GET' });
+    async get<U extends PathsWith<T, 'get'>, M extends keyof T[U]>(url: U, init: FetchOptions<T[U][M]>) {
+      return coreFetch(url, { ...init, method: 'GET' });
     },
     /** Call a PUT endpoint */
-    async put<U extends PathsWith<'put'>, M extends keyof T[U]>(url: U, options: FetchOptions<T[U][M]>) {
-      return coreFetch(url, { ...options, method: 'PUT' });
+    async put<U extends PathsWith<T, 'put'>, M extends keyof T[U]>(url: U, init: FetchOptions<T[U][M]>) {
+      return coreFetch(url, { ...init, method: 'PUT' });
     },
     /** Call a POST endpoint */
-    async post<U extends PathsWith<'post'>, M extends keyof T[U]>(url: U, options: FetchOptions<T[U][M]>) {
-      return coreFetch(url, { ...options, method: 'POST' });
+    async post<U extends PathsWith<T, 'post'>, M extends keyof T[U]>(url: U, init: FetchOptions<T[U][M]>) {
+      return coreFetch(url, { ...init, method: 'POST' });
     },
     /** Call a DELETE endpoint */
-    async del<U extends PathsWith<'delete'>, M extends keyof T[U]>(url: U, options: FetchOptions<T[U][M]>) {
-      return coreFetch(url, { ...options, method: 'DELETE' });
+    async del<U extends PathsWith<T, 'delete'>, M extends keyof T[U]>(url: U, init: FetchOptions<T[U][M]>) {
+      return coreFetch(url, { ...init, method: 'DELETE' });
     },
     /** Call a OPTIONS endpoint */
-    async options<U extends PathsWith<'options'>, M extends keyof T[U]>(url: U, options: FetchOptions<T[U][M]>) {
-      return coreFetch(url, { ...options, method: 'OPTIONS' });
+    async options<U extends PathsWith<T, 'options'>, M extends keyof T[U]>(url: U, init: FetchOptions<T[U][M]>) {
+      return coreFetch(url, { ...init, method: 'OPTIONS' });
     },
     /** Call a HEAD endpoint */
-    async head<U extends PathsWith<'head'>, M extends keyof T[U]>(url: U, options: FetchOptions<T[U][M]>) {
-      return coreFetch(url, { ...options, method: 'HEAD' });
+    async head<U extends PathsWith<T, 'head'>, M extends keyof T[U]>(url: U, init: FetchOptions<T[U][M]>) {
+      return coreFetch(url, { ...init, method: 'HEAD' });
     },
     /** Call a PATCH endpoint */
-    async patch<U extends PathsWith<'patch'>, M extends keyof T[U]>(url: U, options: FetchOptions<T[U][M]>) {
-      return coreFetch(url, { ...options, method: 'PATCH' });
+    async patch<U extends PathsWith<T, 'patch'>, M extends keyof T[U]>(url: U, init: FetchOptions<T[U][M]>) {
+      return coreFetch(url, { ...init, method: 'PATCH' });
     },
     /** Call a TRACE endpoint */
-    async trace<U extends PathsWith<'trace'>, M extends keyof T[U]>(url: U, options: FetchOptions<T[U][M]>) {
-      return coreFetch(url, { ...options, method: 'TRACE' });
+    async trace<U extends PathsWith<T, 'trace'>, M extends keyof T[U]>(url: U, init: FetchOptions<T[U][M]>) {
+      return coreFetch(url, { ...init, method: 'TRACE' });
     },
   };
 }
diff --git a/tsconfig.json b/tsconfig.json
index 0f1fb77..85b111c 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -2,6 +2,7 @@
   "compilerOptions": {
     "allowSyntheticDefaultImports": true,
     "declaration": true,
+    "downlevelIteration": false,
     "esModuleInterop": true,
     "module": "ESNext",
     "moduleResolution": "nodenext",