diff --git a/doc/6-advanced-topics.md b/doc/6-advanced-topics.md
index 4c6a3c671..0e1d73ffa 100644
--- a/doc/6-advanced-topics.md
+++ b/doc/6-advanced-topics.md
@@ -176,6 +176,11 @@ A sample config part can look like this:
       peers = [ "icinga-node-2" ]
     }
 
+> **Note**
+>
+> The certificate files must be readable by the user Icinga 2 is running as. Also,
+> the private key file should not be world-readable.
+
 Peers configures the direction used to connect multiple nodes together. If have
 a three node cluster consisting of