diff --git a/README.md b/README.md
index 4958ab6..e343f43 100644
--- a/README.md
+++ b/README.md
@@ -36,6 +36,7 @@ without an Internet connection.
 
  * [Python](http://www.python.org) 3.6 or later
  * [Transcrypt](https://www.transcrypt.org/) 3.7
+ * [Rollup](https://rollupjs.org/)
 
 
 ### Prepare the build environment