diff --git a/nixbld-etc-nixos/configuration.nix b/nixbld-etc-nixos/configuration.nix
index 06af5cfe..ff093189 100644
--- a/nixbld-etc-nixos/configuration.nix
+++ b/nixbld-etc-nixos/configuration.nix
@@ -952,7 +952,7 @@ in
   };
 
   security.acme.acceptTerms = true;
-  security.acme.defaults.email = "sb" + "@m-labs.hk";
+  security.acme.defaults.email = "sb@m-labs.hk";
 
   # https://github.com/NixOS/nixpkgs/issues/106862
   systemd.services."acme-fixperms".wants = [ "bind.service" "dnsmasq.service" ];