diff --git a/pkgs/development/python-modules/demjson3/default.nix b/pkgs/development/python-modules/demjson3/default.nix
index 1b5b48755912..2c6101fa4d3b 100644
--- a/pkgs/development/python-modules/demjson3/default.nix
+++ b/pkgs/development/python-modules/demjson3/default.nix
@@ -3,12 +3,13 @@
   buildPythonPackage,
   fetchPypi,
   pytestCheckHook,
+  setuptools,
 }:
 
 buildPythonPackage (finalAttrs: {
   pname = "demjson3";
   version = "3.0.6";
-  format = "setuptools";
+  pyproject = true;
 
   __structuredAttrs = true;
 
@@ -17,6 +18,8 @@ buildPythonPackage (finalAttrs: {
     hash = "sha256-N8g7DG6wjSXe/IjfCipIddWKeAmpZQvW7uev2AU826w=";
   };
 
+  build-system = [ setuptools ];
+
   nativeCheckInputs = [ pytestCheckHook ];
 
   pythonImportsCheck = [ "demjson3" ];