diff --git a/.changeset/red-pants-cover.md b/.changeset/red-pants-cover.md
new file mode 100644
index 000000000..7f3bb7429
--- /dev/null
+++ b/.changeset/red-pants-cover.md
@@ -0,0 +1,5 @@
+---
+"openapi-fetch": patch
+---
+
+Let request object have custom properties
diff --git a/packages/openapi-fetch/src/index.d.ts b/packages/openapi-fetch/src/index.d.ts
index 0593075c5..92a36b873 100644
--- a/packages/openapi-fetch/src/index.d.ts
+++ b/packages/openapi-fetch/src/index.d.ts
@@ -166,7 +166,7 @@ export type ClientMethod<Paths extends Record<string, PathMethods>, M extends Ht
   I extends MaybeOptionalInit<Paths[P], M>,
 >(
   url: P,
-  ...init: HasRequiredKeys<I> extends never ? [I?] : [I]
+  ...init: HasRequiredKeys<I> extends never ? [(I & { [key: string]: unknown })?] : [I]
 ) => Promise<FetchResponse<Paths[P][M], I, Media>>;
 
 export default function createClient<Paths extends {}, Media extends MediaType = MediaType>(
diff --git a/packages/openapi-fetch/src/index.js b/packages/openapi-fetch/src/index.js
index c4cede7ef..b2796934a 100644
--- a/packages/openapi-fetch/src/index.js
+++ b/packages/openapi-fetch/src/index.js
@@ -5,6 +5,22 @@ const DEFAULT_HEADERS = {
 
 const PATH_PARAM_RE = /\{[^{}]+\}/g;
 
+/**
+ * Add custom parameters to Request object
+ */
+class CustomRequest extends Request {
+  constructor(input, init) {
+    super(input, init);
+
+    // add custom parameters
+    for (const key in init) {
+      if (!this[key]) {
+        this[key] = init[key];
+      }
+    }
+  }
+}
+
 /**
  * Create an openapi-fetch client.
  * @type {import("./index.js").default}
@@ -67,7 +83,7 @@ export default function createClient(clientOptions) {
     if (requestInit.body instanceof FormData) {
       requestInit.headers.delete("Content-Type");
     }
-    let request = new Request(createFinalURL(url, { baseUrl, params, querySerializer }), requestInit);
+    let request = new CustomRequest(createFinalURL(url, { baseUrl, params, querySerializer }), requestInit);
     // middleware (request)
     const mergedOptions = {
       baseUrl,
diff --git a/packages/openapi-fetch/test/index.test.ts b/packages/openapi-fetch/test/index.test.ts
index f86ab768e..f49979740 100644
--- a/packages/openapi-fetch/test/index.test.ts
+++ b/packages/openapi-fetch/test/index.test.ts
@@ -854,6 +854,29 @@ describe("client", () => {
         expect(req.headers.get("foo")).toBe("bar");
       });
 
+      it("can attach custom properties to request", async () => {
+        function createCustomFetch(data: any) {
+          const response = {
+            clone: () => ({ ...response }),
+            headers: new Headers(),
+            json: async () => data,
+            status: 200,
+            ok: true,
+          } as Response;
+          return async (input: Request) => {
+            expect(input).toHaveProperty("customProperty", "value");
+            return Promise.resolve(response);
+          };
+        }
+
+        const customFetch = createCustomFetch({});
+        const client = createClient<paths>({ fetch: customFetch, baseUrl });
+
+        client.GET("/self", {
+          customProperty: "value",
+        });
+      });
+
       it("can modify response", async () => {
         const toUnix = (date: string) => new Date(date).getTime();