diff --git a/lib/modules/inventoryClass/interface.nix b/lib/modules/inventoryClass/interface.nix
index 4495c7cbf..06c33a4a5 100644
--- a/lib/modules/inventoryClass/interface.nix
+++ b/lib/modules/inventoryClass/interface.nix
@@ -394,6 +394,7 @@ in
                     options = {
                       # ModuleSpec
                       module = lib.mkOption {
+                        default = { };
                         type = types.submodule {
                           options.input = lib.mkOption {
                             type = types.nullOr types.str;