diff --git a/dovecot.nix b/dovecot.nix
index 65e4a6f..83a893b 100644
--- a/dovecot.nix
+++ b/dovecot.nix
@@ -322,7 +322,7 @@ in {
     environment.etc."dovecot/conf.d/admin.conf" = {
       source = cfg.admin-conf;
       user = config.services.dovecot2.user;
-      mode = 400;
+      mode = "400";
     };
 
     services = {