diff --git a/README.md b/README.md
index 2217974..7a5f242 100644
--- a/README.md
+++ b/README.md
@@ -26,7 +26,7 @@ For example, on ubuntu 20.04, you needed to install:
 sudo apt install flex bison byacc make m4
 
 #for support encryption and WS-Security
-sudo apt install openssl libssl-dev libcrypto++6
+sudo apt install openssl libssl-dev zlib1g-dev libcrypto++6
 ```
 
 To start build you have to choose your compiler (or toolchain) in the [Makefile](./Makefile) (see variable `$CC`).