diff --git a/README.txt b/README.txt
index 940cfff273..ee4e28817e 100644
--- a/README.txt
+++ b/README.txt
@@ -387,6 +387,14 @@ Ubuntu Bash under Windows 10
   Many Linux graphics programs would, however, also require a graphics
   framework like GTK or Qt.  So this might be a trip down the rabbit hole.
 
+Using macOS
+----------
+  You need install flock from https://github.com/discoteq/flock
+  before the build start:
+
+    brew tap discoteq/discoteq
+    brew install flock
+
 INSTALLATION
 ^^^^^^^^^^^^