diff --git a/.github/workflows/static.yaml b/.github/workflows/static.yaml
index 66335344c..a367fb94e 100644
--- a/.github/workflows/static.yaml
+++ b/.github/workflows/static.yaml
@@ -44,3 +44,7 @@ jobs:
     - name: Run docs and check extensions
       run: |
         tox -e testdocs
+    
+    - name: Run sphinx extension tests
+      run: |
+        tox -e test-sphinx-ext
diff --git a/.gitignore b/.gitignore
index cfa1c1303..391b674af 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,3 +10,5 @@ _trial_temp/
 apidocs/
 *.egg-info
 .eggs
+.hypothesis
+__pycache__
\ No newline at end of file
diff --git a/pydoctor/sphinx_ext/build_apidocs.py b/pydoctor/sphinx_ext/build_apidocs.py
index 1247e0071..680dc7967 100644
--- a/pydoctor/sphinx_ext/build_apidocs.py
+++ b/pydoctor/sphinx_ext/build_apidocs.py
@@ -67,7 +67,12 @@ def on_build_finished(app: Sphinx, exception: Exception) -> None:
 
         temp_path = output_path.with_suffix('.pydoctor_temp')
         shutil.rmtree(sphinx_files, ignore_errors=True)
-        output_path.rename(sphinx_files)
+        try:
+            output_path.rename(sphinx_files)
+        except FileNotFoundError as e:
+            msg = str(e)
+            msg += '\nMake sur the pydoctor option --html-output is correctly configured.'
+            raise FileNotFoundError(msg) from e
         temp_path.rename(output_path)
 
 
@@ -117,11 +122,11 @@ def on_builder_inited(app: Sphinx) -> None:
 
         # Build the API docs in temporary path.
         shutil.rmtree(temp_path, ignore_errors=True)
-        _run_pydoctor(key,  arguments)
+        _run_pydoctor(key,  arguments, app.warningiserror)
         output_path.rename(temp_path)
 
 
-def _run_pydoctor(name: str, arguments: Sequence[str]) -> None:
+def _run_pydoctor(name: str, arguments: Sequence[str], warningiserror:bool) -> None:
     """
     Call pydoctor with arguments.
 
@@ -135,8 +140,12 @@ def _run_pydoctor(name: str, arguments: Sequence[str]) -> None:
         with redirect_stdout(stream):
             main(args=arguments)
 
+        has_warnings = False
         for line in stream.getvalue().splitlines():
-            logger.warning(line)
+            has_warnings = True
+            logger.info(line)
+        if has_warnings and warningiserror:
+            logger.warning('Pydocor build is not clean and sphinx option -W (turn warnings into errors) is enabled.')
 
 
 def _get_arguments(arguments: Sequence[str], placeholders: Mapping[str, str]) -> Sequence[str]:
diff --git a/pydoctor/test/testpackages/epytext_syntax_error/__init__.py b/pydoctor/test/testpackages/epytext_syntax_error/__init__.py
new file mode 100644
index 000000000..be15f9c7a
--- /dev/null
+++ b/pydoctor/test/testpackages/epytext_syntax_error/__init__.py
@@ -0,0 +1,10 @@
+
+"""
+    Title
+    ~~~~~
+    
+
+    Hello
+    ~~~~~
+"""
+pass
diff --git a/pydoctor/test/testsphinxextension/source/api/index.rst b/pydoctor/test/testsphinxextension/source/api/index.rst
new file mode 100644
index 000000000..b62b2e25a
--- /dev/null
+++ b/pydoctor/test/testsphinxextension/source/api/index.rst
@@ -0,0 +1,2 @@
+API ref
+=======
\ No newline at end of file
diff --git a/pydoctor/test/testsphinxextension/source/conf.py b/pydoctor/test/testsphinxextension/source/conf.py
new file mode 100644
index 000000000..b74bd09f3
--- /dev/null
+++ b/pydoctor/test/testsphinxextension/source/conf.py
@@ -0,0 +1,43 @@
+# Configuration file for the Sphinx documentation builder.
+#
+# For the full list of built-in configuration values, see the documentation:
+# https://www.sphinx-doc.org/en/master/usage/configuration.html
+
+# -- Project information -----------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#project-information
+
+project = 'test-sphinx-ext'
+copyright = '2023, Contributors'
+author = 'Contributors'
+release = '0.0.1'
+
+# -- General configuration ---------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#general-configuration
+
+extensions = []
+templates_path = []
+exclude_patterns = []
+
+# -- Options for HTML output -------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#options-for-html-output
+
+html_theme = 'alabaster'
+html_static_path = []
+
+# ----------------------------------------------------------------------------
+# Test configuration for pydoctor.sphinx_ext.build_apidocs
+
+from pathlib import Path
+extensions.append("pydoctor.sphinx_ext.build_apidocs")
+
+_testpackages = Path(__file__).parent.parent.parent.joinpath('testpackages')
+
+pydoctor_args = [
+    '--project-name=test-sphinx-ext-api',
+    f'--project-version={release}',
+    '--docformat=epytext',
+    '--intersphinx=https://docs.python.org/3/objects.inv',
+    '--html-output={outdir}/api',
+    f'{_testpackages / "report_trigger"}',
+    f'{_testpackages / "epytext_syntax_error"}',
+    ]
\ No newline at end of file
diff --git a/pydoctor/test/testsphinxextension/source/index.rst b/pydoctor/test/testsphinxextension/source/index.rst
new file mode 100644
index 000000000..d85e7a51f
--- /dev/null
+++ b/pydoctor/test/testsphinxextension/source/index.rst
@@ -0,0 +1,21 @@
+.. test-sphinx-ext documentation master file, created by
+   sphinx-quickstart on Thu Oct 26 13:13:53 2023.
+   You can adapt this file completely to your liking, but it should at least
+   contain the root `toctree` directive.
+
+Welcome to test-sphinx-ext's documentation!
+===========================================
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Contents:
+
+   api/index
+
+
+Indices and tables
+==================
+
+* :ref:`genindex`
+* :ref:`modindex`
+* :ref:`search`
diff --git a/pydoctor/test/testsphinxextension/tests/__init__.py b/pydoctor/test/testsphinxextension/tests/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/pydoctor/test/testsphinxextension/tests/test_build_apidocs.py b/pydoctor/test/testsphinxextension/tests/test_build_apidocs.py
new file mode 100644
index 000000000..02baf2b23
--- /dev/null
+++ b/pydoctor/test/testsphinxextension/tests/test_build_apidocs.py
@@ -0,0 +1,19 @@
+import os
+import pathlib
+from typing import List
+import xml.etree.ElementTree as ET
+import json
+
+from pydoctor import __version__
+
+BASE_DIR = pathlib.Path(os.environ.get('TOX_INI_DIR', os.getcwd())) / 'build' / 'test-sphinx-ext'
+
+def test_rtd_pydoctor_call():
+    """
+    With the pydoctor Sphinx extension, the pydoctor API HTML files are
+    generated.
+    """
+    # The pydoctor index is generated and overwrites the Sphinx files.
+    with open(BASE_DIR / 'api' / 'index.html', 'r') as stream:
+        page = stream.read()
+        assert 'moduleIndex.html' in page, page
\ No newline at end of file
diff --git a/tox.ini b/tox.ini
index 706c60f15..c6e2b0f37 100644
--- a/tox.ini
+++ b/tox.ini
@@ -279,3 +279,17 @@ commands =
     echo "::endgroup::"
 
     pytest -vv docs/tests/test.py
+
+[testenv:test-sphinx-ext]
+description = Run integration tests for the sphinx extension
+
+extras = docs
+deps = pytest
+
+setenv =
+    TOX_INI_DIR = {toxinidir}
+
+commands =
+
+    sphinx-build {posargs:} -aE -b html {toxinidir}/pydoctor/test/testsphinxextension/source {toxinidir}/build/test-sphinx-ext
+    pytest -vv {toxinidir}/pydoctor/test/testsphinxextension/tests/test_build_apidocs.py
\ No newline at end of file