diff --git a/pkgs/development/python-modules/twentemilieu/default.nix b/pkgs/development/python-modules/twentemilieu/default.nix
index 1a32eb2cb534..d60db84d68af 100644
--- a/pkgs/development/python-modules/twentemilieu/default.nix
+++ b/pkgs/development/python-modules/twentemilieu/default.nix
@@ -5,6 +5,7 @@
 , aiohttp
 , yarl
 , aresponses
+, poetry-core
 , pytest-asyncio
 , pytestCheckHook
 }:
@@ -12,6 +13,7 @@
 buildPythonPackage rec {
   pname = "twentemilieu";
   version = "0.4.2";
+  format = "pyproject";
   disabled = pythonOlder "3.7";
 
   src = fetchFromGitHub {
@@ -21,6 +23,16 @@ buildPythonPackage rec {
     sha256 = "1lf31ldbrsmxhbrcg284pwpvjfmwnssv3gqwd5vm2hvd9lwqn6ii";
   };
 
+  # coverage tests aren't useful when consuming releases
+  postPatch = ''
+    substituteInPlace pyproject.toml \
+      --replace '--cov' ""
+  '';
+
+  nativeBuildInputs = [
+    poetry-core
+  ];
+
   propagatedBuildInputs = [
     aiohttp
     yarl