diff --git a/.changeset/warm-plums-wait.md b/.changeset/warm-plums-wait.md
new file mode 100644
index 000000000..00361e0e8
--- /dev/null
+++ b/.changeset/warm-plums-wait.md
@@ -0,0 +1,5 @@
+---
+"openapi-fetch": patch
+---
+
+Allow FormData through defaultBodySerializer
diff --git a/packages/openapi-fetch/src/index.js b/packages/openapi-fetch/src/index.js
index cdcc3052e..e878ef0b8 100644
--- a/packages/openapi-fetch/src/index.js
+++ b/packages/openapi-fetch/src/index.js
@@ -434,6 +434,9 @@ export function defaultPathSerializer(pathname, pathParams) {
  * @type {import("./index.js").defaultBodySerializer}
  */
 export function defaultBodySerializer(body) {
+  if (body instanceof FormData) {
+    return body;
+  }
   return JSON.stringify(body);
 }
 
diff --git a/packages/openapi-fetch/test/fixtures/api.d.ts b/packages/openapi-fetch/test/fixtures/api.d.ts
index cad5160d4..b1675777c 100644
--- a/packages/openapi-fetch/test/fixtures/api.d.ts
+++ b/packages/openapi-fetch/test/fixtures/api.d.ts
@@ -814,6 +814,46 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/multipart-form-data-file-upload": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get?: never;
+        put?: never;
+        post: {
+            parameters: {
+                query?: never;
+                header?: never;
+                path?: never;
+                cookie?: never;
+            };
+            requestBody: {
+                content: {
+                    "multipart/form-data": string;
+                };
+            };
+            responses: {
+                200: {
+                    headers: {
+                        [name: string]: unknown;
+                    };
+                    content: {
+                        "application/json": {
+                            text: string;
+                        };
+                    };
+                };
+            };
+        };
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
 }
 export type webhooks = Record<string, never>;
 export interface components {
diff --git a/packages/openapi-fetch/test/fixtures/api.yaml b/packages/openapi-fetch/test/fixtures/api.yaml
index 8994e1ba8..011fcc768 100644
--- a/packages/openapi-fetch/test/fixtures/api.yaml
+++ b/packages/openapi-fetch/test/fixtures/api.yaml
@@ -470,6 +470,26 @@ paths:
       responses:
         200:
           $ref: "#/components/responses/MultipleResponse"
+  /multipart-form-data-file-upload:
+    post:
+      requestBody:
+        content:
+          multipart/form-data:
+            schema:
+              type: string
+              format: binary
+        required: true
+      responses:
+        "200":
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  text:
+                    type: string
+                required:
+                  - text
 components:
   schemas:
     Post:
diff --git a/packages/openapi-fetch/test/index.test.ts b/packages/openapi-fetch/test/index.test.ts
index 687bdc957..0055dcba7 100644
--- a/packages/openapi-fetch/test/index.test.ts
+++ b/packages/openapi-fetch/test/index.test.ts
@@ -1352,6 +1352,33 @@ describe("client", () => {
         customProperty: "value",
       });
     });
+
+    it("multipart/form-data with a file", async () => {
+      const TEST_STRING = "Hello this is text file string";
+
+      const file = new Blob([TEST_STRING], { type: "text/plain" });
+      const formData = new FormData();
+      formData.append("file", file);
+
+      const client = createClient<paths>({ baseUrl });
+      useMockRequestHandler({
+        baseUrl,
+        method: "post",
+        path: "/multipart-form-data-file-upload",
+        handler: async (data) => {
+          // Get text from file and send it back
+          const formData = await data.request.formData();
+          const text = await (formData.get("file") as File).text();
+          return new HttpResponse(JSON.stringify({ text }));
+        },
+      });
+      const { data } = await client.POST("/multipart-form-data-file-upload", {
+        // TODO: how to get this to accept FormData?
+        body: formData as unknown as string,
+      });
+
+      expect(data?.text).toBe(TEST_STRING);
+    });
   });
 
   describe("responses", () => {