diff --git a/nixbld-etc-nixos/configuration.nix b/nixbld-etc-nixos/configuration.nix
index ec9008c..b129e67 100644
--- a/nixbld-etc-nixos/configuration.nix
+++ b/nixbld-etc-nixos/configuration.nix
@@ -427,6 +427,7 @@ in
   security.acme.email = "sb" + "@m-labs.hk";
   security.acme.certs = {
     "nixbld.m-labs.hk" = {
+      group = "nginx";
       webroot = "/var/lib/acme/acme-challenge";
       extraDomainNames = [
         "m-labs.hk"