diff --git a/README.md b/README.md
index 47724fe..4c2e84a 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 [![Build Status](https://jenkins.timshome.page/buildStatus/icon?job=timw4mail%2Fphp-kilo%2Fmaster)](https://jenkins.timshome.page/job/timw4mail/job/php-kilo/job/master/)
 
-A reimplementation of the [Kilo](https://viewsourcecode.org/snaptoken/kilo/index.html) tutorial in PHP. Requires PHP 8.
+A reimplementation of the [Kilo](https://viewsourcecode.org/snaptoken/kilo/index.html) tutorial in PHP. Requires PHP 8 and FFI.
 
 ## Implementation notes: