diff --git a/src/index.test.ts b/src/index.test.ts
index e5ab94d..c896413 100644
--- a/src/index.test.ts
+++ b/src/index.test.ts
@@ -351,6 +351,42 @@ describe('post()', () => {
     // assert error is empty
     expect(error).toBe(undefined);
   });
+
+  it('request body type when optional', async() => {
+    fetchMocker.mockResponse(() => ({ status: 201, body: '{}' }));
+    const client = createClient<paths>();
+
+    // expect error on wrong body type
+    // @ts-expect-error
+    await client.post('/post/optional', { body: { error: true } })
+
+    // (no error)
+    await client.post('/post/optional', {
+      body: {
+        title: '',
+        publish_date: 3,
+        body: ''
+      }
+    })
+  })
+
+  it('request body type when optional inline', async() => {
+    fetchMocker.mockResponse(() => ({ status: 201, body: '{}' }));
+    const client = createClient<paths>();
+
+    // expect error on wrong body type
+    // @ts-expect-error
+    await client.post('/post/optional/inline', { body: { error: true } })
+
+    // (no error)
+    await client.post('/post/optional/inline', {
+      body: {
+        title: '',
+        publish_date: 3,
+        body: ''
+      }
+    })
+  })
 });
 
 describe('delete()', () => {
diff --git a/src/index.ts b/src/index.ts
index b8e6582..6373e92 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -34,16 +34,19 @@ export type FilterKeys<Obj, Matchers> = { [K in keyof Obj]: K extends Matchers ?
 /** handle "application/json", "application/vnd.api+json", "appliacation/json;charset=utf-8" and more */
 export type JSONLike = `${string}json${string}`;
 
-// fetch types
+// general purpose types
 export type Params<O> = O extends { parameters: any } ? { params: NonNullable<O['parameters']> } : BaseParams;
-export type RequestBodyObj<O> = O extends { requestBody: any } ? O['requestBody'] : never;
+export type RequestBodyObj<O> = O extends { requestBody?: any } ? O['requestBody'] : never;
 export type RequestBodyContent<O> = undefined extends RequestBodyObj<O> ? FilterKeys<NonNullable<RequestBodyObj<O>>, 'content'> | undefined : FilterKeys<RequestBodyObj<O>, 'content'>;
 export type RequestBodyJSON<O> = FilterKeys<RequestBodyContent<O>, JSONLike> extends never ? FilterKeys<NonNullable<RequestBodyContent<O>>, JSONLike> | undefined : FilterKeys<RequestBodyContent<O>, JSONLike>;
 export type RequestBody<O> = undefined extends RequestBodyJSON<O> ? { body?: RequestBodyJSON<O> } : { body: RequestBodyJSON<O> };
 export type QuerySerializer<O> = (query: O extends { parameters: { query: any } } ? O['parameters']['query'] : Record<string, unknown>) => string;
-export type FetchOptions<T> = Params<T> & RequestBody<T> & Omit<RequestInit, 'body'> & { querySerializer?: QuerySerializer<T> };
+export type RequestOptions<T> = Params<T> & RequestBody<T> & { querySerializer?: QuerySerializer<T> };
 export type Success<O> = FilterKeys<FilterKeys<O, OkStatus>, 'content'>;
 export type Error<O> = FilterKeys<FilterKeys<O, ErrorStatus>, 'content'>;
+
+// fetch types
+export type FetchOptions<T> = RequestOptions<T> & Omit<RequestInit, 'body'>;
 export type FetchResponse<T> =
   | { data: T extends { responses: any } ? NonNullable<FilterKeys<Success<T['responses']>, JSONLike>> : unknown; error?: never; response: Response }
   | { data?: never; error: T extends { responses: any } ? NonNullable<FilterKeys<Error<T['responses']>, JSONLike>> : unknown; response: Response };
diff --git a/test/v1.d.ts b/test/v1.d.ts
index 340ee5e..d5a455f 100644
--- a/test/v1.d.ts
+++ b/test/v1.d.ts
@@ -23,6 +23,28 @@ export interface paths {
       };
     };
   };
+  "/post/optional": {
+    post: {
+      requestBody: components["requestBodies"]["CreatePostOptional"];
+      responses: {
+        201: components["responses"]["CreatePost"];
+        500: components["responses"]["Error"];
+      };
+    };
+  };
+  "/post/optional/inline": {
+    post: {
+      requestBody?: {
+        content: {
+          "application/json": components["schemas"]["Post"];
+        };
+      };
+      responses: {
+        201: components["responses"]["CreatePost"];
+        500: components["responses"]["Error"];
+      };
+    };
+  };
   "/posts": {
     get: {
       responses: {
@@ -271,6 +293,15 @@ export interface components {
         };
       };
     };
+    CreatePostOptional?: {
+      content: {
+        "application/json": {
+          title: string;
+          body: string;
+          publish_date: number;
+        };
+      };
+    };
     CreateTag?: {
       content: {
         "application/json": {
diff --git a/test/v1.yaml b/test/v1.yaml
index ec8bd58..d1c8277 100644
--- a/test/v1.yaml
+++ b/test/v1.yaml
@@ -1,4 +1,6 @@
-openapi:
+openapi: 3.0.3
+info:
+  title: Test Specification
   version: '3.1'
 paths:
   /comment:
@@ -19,6 +21,27 @@ paths:
           $ref: '#/components/responses/CreatePost'
         500:
           $ref: '#/components/responses/Error'
+  /post/optional:
+    post:
+      requestBody:
+        $ref: '#/components/requestBodies/CreatePostOptional'
+      responses:
+        201:
+          $ref: '#/components/responses/CreatePost'
+        500:
+          $ref: '#/components/responses/Error'
+  /post/optional/inline:
+    post:
+      requestBody:
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/Post'
+      responses:
+        201:
+          $ref: '#/components/responses/CreatePost'
+        500:
+          $ref: '#/components/responses/Error'
   /posts:
     get:
       responses:
@@ -214,6 +237,23 @@ components:
               - title
               - body
               - publish_date
+    CreatePostOptional:
+      required: false
+      content:
+        application/json:
+          schema:
+            type: object
+            properties:
+              title:
+                type: string
+              body:
+                type: string
+              publish_date:
+                type: number
+            required:
+              - title
+              - body
+              - publish_date
     CreateTag:
       content:
         application/json: