diff --git a/README.md b/README.md
index 74a28b4..e0026e4 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,7 @@
 # `zmq-fileserver`
 
 This is a simple fileserver written in PHP (7.4+) using [ZeroMQ](https://zeromq.org/).  
+It requires `ext-zmq` and PHP7.4+.  
 
 There are three executable files:
 - `$ bin/server` runs the fileserver