diff --git a/lib/index.ts b/lib/index.ts
index 51ace59..6a27198 100644
--- a/lib/index.ts
+++ b/lib/index.ts
@@ -189,13 +189,13 @@ export class Client {
     if (args.cookieJar) {
       const cookie = args.cookieJar.getCookieStringSync(url)
 
-      options.headers = { ...args.headers, Cookie: cookie }
+      options.headers = { ...options.headers, Cookie: cookie }
     }
 
     if (args.body?.constructor.name === 'FormData') {
-      options.headers = (<FormData> args.body).getHeaders(args.headers)
+      options.headers =  (args.body as FormData).getHeaders(options.headers)
 
-      options.body = (<FormData> args.body).getBuffer()
+      options.body = (args.body as FormData).getBuffer()
     }
 
     const res: Response<T> = await requestPromise.call(this.#client, url, options)
diff --git a/src/client.rs b/src/client.rs
index 49f85e5..8b7a7f6 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -273,8 +273,13 @@ impl Client {
             DataType::Binary(v) if v.is_some() => {
                 let val = v.unwrap();
 
-                let mut buf= JsBuffer::new(cx, val.len())?;
-                buf.as_mut_slice(cx).copy_from_slice(&val);
+                let mut buf= JsBuffer::new(cx, val.len()).unwrap();
+
+                let lock = cx.lock();
+                match buf.try_borrow_mut(&lock) {
+                    Ok(mut dest) => dest.copy_from_slice(&val),
+                    Err(error) => log::error!("Error while copying buffer: {:?}", error)
+                }
 
                 obj.set(cx, "body", buf)?;
             }