diff --git a/lib/builders.nix b/lib/builders.nix
index 0f69e95..2d2aef6 100644
--- a/lib/builders.nix
+++ b/lib/builders.nix
@@ -31,6 +31,7 @@ rec {
       configHost = if builtins.stringLength configHostname > 0 then configHostname else hostname;
       hostStr = lib.strings.optionalString (builtins.stringLength hostname > 0) "@${hostname}";
     in
+    assert lib.assertMsg (builtins.stringLength configHost > 0) "either configHostname or hostname need to exist";
     {
       name = "${user}${hostStr}";
       value = inputs.home-manager.lib.homeManagerConfiguration {