diff --git a/lib/node-progress.js b/lib/node-progress.js
index 8eb0740..167c544 100644
--- a/lib/node-progress.js
+++ b/lib/node-progress.js
@@ -75,8 +75,8 @@ function ProgressBar(fmt, options) {
 /**
  * "tick" the progress bar with optional `len` and optional `tokens`.
  *
- * @param {number|object} len or tokens
- * @param {object} tokens
+ * @param {number|object} [len] or tokens
+ * @param {object} [tokens]
  * @api public
  */