diff --git a/.github/workflows/pytest.yaml b/.github/workflows/pytest.yaml
index c33ba83b..eca94603 100644
--- a/.github/workflows/pytest.yaml
+++ b/.github/workflows/pytest.yaml
@@ -22,6 +22,11 @@ jobs:
         uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
+      - name: Install oldest versions of supported dependencies
+        if: ${{ matrix.python-version == "3.9"}}
+        # Changes to these dependencies must be updated
+        # in pyproject.toml and docs/install.rst
+        run: pip install numpy==1.22 scipy==1.8 attrs==21.3.0
       - name: Install development version
         run: pip install -e .[dev]
       - name: Run Pytest
diff --git a/doc/install.rst b/doc/install.rst
index 7b363751..b287994b 100644
--- a/doc/install.rst
+++ b/doc/install.rst
@@ -30,6 +30,10 @@ Latest PyPI version
 Python 3 (>=3.9) must be installed before you can install IOData.
 In addition, IOData has the following dependencies:
 
+..
+    Changes to these dependencies must be updated
+    in pyproject.toml and .github/workfloews/pytest.yaml
+
 - numpy >= 1.22: https://numpy.org/
 - scipy >= 1.8: https://scipy.org/
 - attrs >= 21.3.0: https://www.attrs.org/en/stable/index.html
diff --git a/pyproject.toml b/pyproject.toml
index eeed55f7..3b050890 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -29,6 +29,8 @@ classifiers = [
     "Topic :: Scientific/Engineering :: Chemistry",
 ]
 dependencies = [
+    # Changes to these dependencies must be updated
+    # in .github/workfloews/pytest.yaml and docs/install.rst
     "numpy>=1.22",
     "scipy>=1.8",
     "attrs>=21.3.0",
@@ -47,7 +49,7 @@ Source = "https://github.com/theochem/iodata/"
 iodata-convert = "iodata.__main__:main"
 
 [tool.pytest.ini_options]
-addopts = "-n auto"
+addopts = "-n auto -W error"
 
 [tool.setuptools]
 packages = ["iodata"]