diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index f7dbaf6..834b36d 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -143,12 +143,16 @@ jobs:
         python-version: ${{ env.DEFAULT_PYTHON_VERSION }}
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pydoctor
+        python -m pip install --upgrade pydoctor sphinx
 
     - name: Run pydoctor
       run: |
         pydoctor --project-name constantly constantly
 
+    - name: Run Sphinx
+      run: |
+        sphinx-build -W -b html docs/ docs/_build/html
+
 
   # Used for various release automation.
   # This is also executed for each PR to exercise the release as much
diff --git a/docs/conf.py b/docs/conf.py
index 17f81b1..989e5d2 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -70,7 +70,7 @@
 #
 # This is also used if you do content translation via gettext catalogs.
 # Usually you set "language" from the command line for these cases.
-language = None
+language = "en"
 
 # There are two options for replacing |today|: either, you set today to some
 # non-false value, then it is used:
@@ -291,4 +291,4 @@
 
 
 # Example configuration for intersphinx: refer to the Python standard library.
-intersphinx_mapping = {'https://docs.python.org/': None}
+intersphinx_mapping = {'python': ('https://docs.python.org/3', None)}