diff --git a/changelog.d/9464.misc b/changelog.d/9464.misc
new file mode 100644
index 0000000000..39fcf85d40
--- /dev/null
+++ b/changelog.d/9464.misc
@@ -0,0 +1 @@
+Add a comment about systemd-python.
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 8a2b73b75e..321a333820 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -106,6 +106,9 @@ CONDITIONAL_REQUIREMENTS = {
         "pysaml2>=4.5.0;python_version>='3.6'",
     ],
     "oidc": ["authlib>=0.14.0"],
+    # systemd-python is necessary for logging to the systemd journal via
+    # `systemd.journal.JournalHandler`, as is documented in
+    # `contrib/systemd/log_config.yaml`.
     "systemd": ["systemd-python>=231"],
     "url_preview": ["lxml>=3.5.0"],
     "sentry": ["sentry-sdk>=0.7.2"],