diff --git a/README.md b/README.md
index d2a3868..61c070f 100644
--- a/README.md
+++ b/README.md
@@ -25,7 +25,9 @@ You should be familiar with linux and should be able to edit files with `vi` [Vi
 You need an USB stick for the Linux Live environment and a second computer would be useful for look ups and to read this guide while
 preparing your fully encrypted Linux.
 
-And of course you will need an [YubiKey](https://www.yubico.com/products/yubikey-hardware/ "Discover YubiKeys").
+And of course you will need at least **two** [YubiKeys](https://www.yubico.com/products/yubikey-hardware/ "Discover YubiKeys").  
+
+**WARNING:** You gonna get a bricked machine if you only have a single Yubikey and it breaks.
 
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