diff --git a/docs/conf.py b/docs/conf.py
index b7bbda8..0791a4e 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -13,8 +13,17 @@
 # the License.
 """Pigweed's Sphinx configuration."""
 
+import sphinx
 import sphinx_rtd_theme
 
+# TODO(pwbug/376): Remove this when this PR is merged:
+# https://github.com/mgaitan/sphinxcontrib-mermaid/pull/71
+# Needed for sphinxcontrib-mermaid compatibility with sphinx 4.0.0.
+if sphinx.version_info[0] >= 4:
+    import errno
+    import sphinx.util.osutil
+    sphinx.util.osutil.ENOENT = errno.ENOENT
+
 # The suffix of source filenames.
 source_suffix = ['.rst']