diff --git a/README.md b/README.md
index 49fbc45..fb02335 100644
--- a/README.md
+++ b/README.md
@@ -186,6 +186,8 @@ Outputs:
 cert-authority,principals="root" ecdsa-sha2-nistp384 AAAAE2VjZHNh****** Yubikey-PIV-R15
 ```
 
+> `principals` can be multiple items, split by ',', e.g. `root,hatterink`
+
 ## Generate SSH user CA
 
 ```shell