diff --git a/lib/jsonschema/default.nix b/lib/jsonschema/default.nix
index df3f63b8..ea089d2a 100644
--- a/lib/jsonschema/default.nix
+++ b/lib/jsonschema/default.nix
@@ -65,6 +65,7 @@ rec {
     required
     // {
       type = "object";
+      additionalProperties = false;
       inherit properties;
     };