diff --git a/src/Checkout.js b/src/Checkout.js
index 9c68f93..6acc5b9 100644
--- a/src/Checkout.js
+++ b/src/Checkout.js
@@ -198,9 +198,9 @@ export class Checkout {
     /**
      * Add an event listener for a specific `event`
      * @param {string} event Event name to listen
-     * @param {string} callback Callback function to call when event triggers
+     * @param {function} callback Callback function to call when event triggers
      */
     on(event, callback){
         document.addEventListener(`checkout:${event}`, callback, false);
     }
-}
\ No newline at end of file
+}