diff --git a/doc/redis.md b/doc/redis.md
index 8d964b2..80df24c 100644
--- a/doc/redis.md
+++ b/doc/redis.md
@@ -3,6 +3,8 @@
 
 0) Install redis
 
+Redis 3.x or higher is required
+
 0.A) debian/ubuntu
 
     # apt update