diff --git a/lib/composite.js b/lib/composite.js
index 11114673..46dcdd0a 100644
--- a/lib/composite.js
+++ b/lib/composite.js
@@ -26,7 +26,7 @@ const is = require('./is');
  *     // sharpened, with metadata, 90% quality WebP image data. Phew!
  *   });
  *
- * @param {(Buffer|String)} overlay - Buffer containing image data or String containing the path to an image file.
+ * @param {(Buffer|String)} [overlay] - Buffer containing image data or String containing the path to an image file.
  * @param {Object} [options]
  * @param {String} [options.gravity='centre'] - gravity at which to place the overlay.
  * @param {Number} [options.top] - the pixel offset from the top edge.