diff --git a/backend/tests/test_backend_contracts.py b/backend/tests/test_backend_contracts.py
index 15bf3a1..ccc2740 100644
--- a/backend/tests/test_backend_contracts.py
+++ b/backend/tests/test_backend_contracts.py
@@ -92,6 +92,7 @@ def test_backend_src_path_is_self_contained(tmp_path):
     result = subprocess.run(
         [sys.executable, "-c", code],
         cwd=tmp_path,
+        env={**os.environ, "PYTHONPATH": str(Path(__file__).resolve().parents[1] / "src")},
         env=env,
         text=True,
         capture_output=True,