diff --git a/pkgs/development/python-modules/xml2rfc/default.nix b/pkgs/development/python-modules/xml2rfc/default.nix
index 34dc6116a3f1..84129e8a27d4 100644
--- a/pkgs/development/python-modules/xml2rfc/default.nix
+++ b/pkgs/development/python-modules/xml2rfc/default.nix
@@ -22,13 +22,14 @@
   pythonOlder,
   pyyaml,
   requests,
+  setuptools,
   wcwidth,
 }:
 
 buildPythonPackage rec {
   pname = "xml2rfc";
   version = "3.23.2";
-  format = "setuptools";
+  pyproject = true;
 
   disabled = pythonOlder "3.8";
 
@@ -45,7 +46,11 @@ buildPythonPackage rec {
       --replace-fail "test flaketest" "test"
   '';
 
-  propagatedBuildInputs = [
+  build-system = [ setuptools ];
+
+  pythonRelaxDeps = [ "lxml" ];
+
+  dependencies = [
     appdirs
     configargparse
     dict2xml