diff --git a/conf.py b/conf.py
index 37e4f7b5bf2..3d39d1182be 100644
--- a/conf.py
+++ b/conf.py
@@ -8,6 +8,11 @@
 
 sys.path.append(str(Path("pep_sphinx_extensions").absolute()))
 
+# Add 'include_patterns' as a config variable
+from sphinx.config import Config
+Config.config_values['include_patterns'] = [], 'env', []
+del Config
+
 # -- Project information -----------------------------------------------------
 
 project = "PEPs"
@@ -25,24 +30,20 @@
 }
 
 # List of patterns (relative to source dir) to ignore when looking for source files.
+include_patterns = [
+    # Required for Sphinx
+    "contents.rst",
+    # PEP files
+    "pep-????.rst",
+    "pep-????.txt",
+    # PEP ancillary files
+    "pep-????/*.rst",
+    # Documentation
+    "docs/*.rst",
+]
 exclude_patterns = [
-    # Windows:
-    "Thumbs.db",
-    ".DS_Store",
-    # Python:
-    ".venv",
-    "venv",
-    "requirements.txt",
-    # Sphinx:
-    "build",
-    "output.txt",  # Link-check output
-    # PEPs:
-    "pep-0012",
-    "README.rst",
-    "CONTRIBUTING.rst",
-    "pep_sphinx_extensions/LICENCE.rst",
-    # Miscellaneous
-    ".codespell",
+    # PEP Template
+    "pep-0012/pep-NNNN.rst",
 ]
 
 # -- Options for HTML output -------------------------------------------------
diff --git a/pep_sphinx_extensions/__init__.py b/pep_sphinx_extensions/__init__.py
index e9d366ca196..d1726975a31 100644
--- a/pep_sphinx_extensions/__init__.py
+++ b/pep_sphinx_extensions/__init__.py
@@ -6,6 +6,7 @@
 
 from docutils.writers.html5_polyglot import HTMLTranslator
 from sphinx import environment
+from sphinx import project
 
 from pep_sphinx_extensions.pep_processor.html import pep_html_builder
 from pep_sphinx_extensions.pep_processor.html import pep_html_translator
@@ -16,6 +17,37 @@
 
 if TYPE_CHECKING:
     from sphinx.application import Sphinx
+    from sphinx.config import Config
+
+
+def find_files(self: environment.BuildEnvironment, config: Config, _b) -> None:
+    """Find all pep source files."""
+    import fnmatch
+    from pathlib import Path
+
+    root = Path(self.project.srcdir).absolute()
+    self.project.docnames = set()
+    for pattern in config.include_patterns:
+        for path in root.glob(pattern):
+            filename = str(path.relative_to(root))
+            if any(fnmatch.fnmatch(filename, pattern) for pattern in config.exclude_patterns):
+                continue
+
+            doc_name = self.project.path2doc(filename)
+            if not doc_name:
+                continue
+
+            if doc_name not in self.project.docnames:
+                self.project.docnames.add(doc_name)
+                continue
+
+            other_files = [str(f.relative_to(root)) for f in root.glob(f"{doc_name}.*")]
+            project.logger.warning(
+                f'multiple files found for the document "{doc_name}": {other_files!r}\n'
+                f'Use {self.doc2path(doc_name)!r} for the build.', once=True)
+
+
+environment.BuildEnvironment.find_files = find_files
 
 
 def _depart_maths():