diff --git a/README.md b/README.md
index 8b4625b..f64a495 100644
--- a/README.md
+++ b/README.md
@@ -4,3 +4,5 @@ This repository contains files needed to run Lite XL in the browser.
 Lite XL includes a shell file that does the job pretty well,
 but the aim here is to improve the experience more by making it actually
 useful.
+
+You will need to use Emscripten 3.1.57. Older versions may not work.