diff --git a/hugr-py/pyproject.toml b/hugr-py/pyproject.toml
index 28e4652b7..b655b3f9d 100644
--- a/hugr-py/pyproject.toml
+++ b/hugr-py/pyproject.toml
@@ -30,3 +30,7 @@ pydantic = "~2.7.0"
 [tool.pytest.ini_options]
 # Lark throws deprecation warnings for `src_parse` and `src_constants`.
 filterwarnings = "ignore::DeprecationWarning:lark.*"
+
+[build-system]
+requires = ["poetry-core"]
+build-backend = "poetry.core.masonry.api"