diff --git a/.github/workflows/ci_tests.yml b/.github/workflows/ci_tests.yml
index c7ae700..47f4688 100644
--- a/.github/workflows/ci_tests.yml
+++ b/.github/workflows/ci_tests.yml
@@ -104,6 +104,13 @@ jobs:
             allow_failure: true
             prefix: '(Allowed failure)'
 
+          - os: ubuntu-latest
+            python: '3.12-dev'
+            tox_env: 'py312-test-devdeps'
+            toxposargs: --remote-data=any
+            allow_failure: true
+            prefix: '(Allowed failure)'
+
     steps:
     - name: Check out repository
       uses: actions/checkout@v4
@@ -114,9 +121,7 @@ jobs:
       with:
         python-version: ${{ matrix.python }}
     - name: Install base dependencies
-      run: |
-        python -m pip install --upgrade pip
-        python -m pip install tox
+      run: python -m pip install --upgrade pip setuptools tox
     - name: Print Python, pip, setuptools, and tox versions
       run: |
         python -c "import sys; print(f'Python {sys.version}')"
diff --git a/pyproject.toml b/pyproject.toml
index 3df119c..8037e6a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -91,6 +91,8 @@ filterwarnings = [
     'error',  # turn warnings into exceptions
     'ignore:numpy.ufunc size changed:RuntimeWarning',
     'ignore:numpy.ndarray size changed:RuntimeWarning',
+    # python 3.12 deprecation in matplotlib 3.9dev
+    'ignore:datetime.datetime.utcfromtimestamp\(\) is deprecated:DeprecationWarning',
 ]
 
 [tool.coverage.run]
diff --git a/tox.ini b/tox.ini
index 6907469..3d9cda1 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,7 @@
 [tox]
 envlist =
-    py{39,310,311}-test{,-alldeps,-devdeps,-oldestdeps,-devinfra}{,-cov}
-    py{39,310,311}-test-numpy{122,123,124,125,126}
+    py{39,310,311,312}-test{,-alldeps,-devdeps,-oldestdeps,-devinfra}{,-cov}
+    py{39,310,311,312}-test-numpy{122,123,124,125,126}
     build_docs
     linkcheck
     codestyle
@@ -16,7 +16,7 @@ isolated_build = true
 # Suppress display of matplotlib plots generated during docs build
 setenv =
     MPLBACKEND=agg
-    devdeps: PIP_EXTRA_INDEX_URL = https://pypi.anaconda.org/scientific-python-nightly-wheels/simple https://pypi.anaconda.org/astropy/simple
+    devdeps: PIP_EXTRA_INDEX_URL = https://pypi.anaconda.org/scientific-python-nightly-wheels/simple
 
 # Pass through the following environment variables which may be needed
 # for the CI
@@ -83,6 +83,9 @@ extras =
     build_docs: docs
 
 commands =
+    # Force numpy-dev after matplotlib downgrades it
+    # (https://github.com/matplotlib/matplotlib/issues/26847)
+    devdeps: python -m pip install --pre --upgrade --extra-index-url https://pypi.anaconda.org/scientific-python-nightly-wheels/simple numpy
     pip freeze
     pytest --pyargs lacosmic {toxinidir}/docs \
     cov: --cov lacosmic --cov-config={toxinidir}/pyproject.toml --cov-report xml:{toxinidir}/coverage.xml --cov-report term-missing \