diff --git a/README.md b/README.md
index 35b583f..64c7f17 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,7 @@ Tested on:
 
 ## Requirements:
 * Zabbix v6.4 or later
+* whois (GNU utils)
 
 ## Setup: