diff --git a/index.js b/index.js
index f7cbdf00..1bef2072 100644
--- a/index.js
+++ b/index.js
@@ -75,7 +75,8 @@ function load(filename) {
 
 /**
  * Get a function that a client can use to update metadata with authentication
- * information from a Google Auth credential object.
+ * information from a Google Auth credential object, which comes from the
+ * googleauth library.
  * @param {Object} credential The credential object to use
  * @return {function(Object, callback)} Metadata updater function
  */