diff --git a/pkgs/development/python-modules/testing-postgresql/default.nix b/pkgs/development/python-modules/testing-postgresql/default.nix
index c2b85fe8f9d7..1b16def31580 100644
--- a/pkgs/development/python-modules/testing-postgresql/default.nix
+++ b/pkgs/development/python-modules/testing-postgresql/default.nix
@@ -2,6 +2,7 @@
   lib,
   buildPythonPackage,
   fetchFromGitHub,
+  setuptools,
   pg8000,
   postgresql,
   psycopg2,
@@ -15,7 +16,7 @@ buildPythonPackage rec {
   pname = "testing-postgresql";
   # Version 1.3.0 isn't working so let's use the latest commit from GitHub
   version = "unstable-2017-10-31";
-  format = "setuptools";
+  pyproject = true;
 
   disabled = pythonOlder "3.7";
 
@@ -26,7 +27,9 @@ buildPythonPackage rec {
     hash = "sha256-A4tahAaa98X66ZYa3QxIQDZkwAwVB6ZDRObEhkbUWKs=";
   };
 
-  propagatedBuildInputs = [
+  build-system = [ setuptools ];
+
+  dependencies = [
     testing-common-database
     pg8000
   ];
@@ -40,12 +43,14 @@ buildPythonPackage rec {
   # Add PostgreSQL to search path
   prePatch = ''
     substituteInPlace src/testing/postgresql.py \
-      --replace "/usr/local/pgsql" "${postgresql}"
+      --replace-fail "/usr/local/pgsql" "${postgresql}"
   '';
 
+  pythonRelaxDeps = [ "pg8000" ];
+
   postPatch = ''
     substituteInPlace setup.py \
-      --replace "pg8000 >= 1.10" "pg8000"
+      --replace-fail "pg8000 >= 1.10" "pg8000"
     substituteInPlace tests/test_postgresql.py \
       --replace-fail "self.assertRegexpMatches" "self.assertRegex"
   '';