diff --git a/setup.cfg b/setup.cfg
index 441c69d..f43f807 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -40,6 +40,7 @@ include_package_data = True
 [options.extras_require]
 testing =
     tox
+    numpy
     pytest  # https://docs.pytest.org/en/latest/contents.html
     pytest-cov  # https://pytest-cov.readthedocs.io/en/latest/
     zarr