diff --git a/changelog.d/15909.misc b/changelog.d/15909.misc
new file mode 100644
index 000000000..ba36a9744
--- /dev/null
+++ b/changelog.d/15909.misc
@@ -0,0 +1 @@
+Document which Python version runs on a given Linux distribution so we can more easily clean up later.
diff --git a/scripts-dev/build_debian_packages.py b/scripts-dev/build_debian_packages.py
index 8fe10f2cb..195483547 100755
--- a/scripts-dev/build_debian_packages.py
+++ b/scripts-dev/build_debian_packages.py
@@ -22,14 +22,18 @@ from typing import Collection, Optional, Sequence, Set
 
 # These are expanded inside the dockerfile to be a fully qualified image name.
 # e.g. docker.io/library/debian:bullseye
+#
+# If an EOL is forced by a Python version and we're dropping support for it, make sure
+# to remove references to the distibution across Synapse (search for "bullseye" for
+# example)
 DISTS = (
-    "debian:bullseye",
-    "debian:bookworm",
-    "debian:sid",
-    "ubuntu:focal",  # 20.04 LTS (our EOL forced by Py38 on 2024-10-14)
-    "ubuntu:jammy",  # 22.04 LTS (EOL 2027-04)
-    "ubuntu:kinetic",  # 22.10 (EOL 2023-07-20)
-    "ubuntu:lunar",  # 23.04 (EOL 2024-01)
+    "debian:bullseye",  # (EOL ~2024-07) (our EOL forced by Python 3.9 is 2025-10-05)
+    "debian:bookworm",  # (EOL not specified yet) (our EOL forced by Python 3.11 is 2027-10-24)
+    "debian:sid",  # (EOL not specified yet) (our EOL forced by Python 3.11 is 2027-10-24)
+    "ubuntu:focal",  # 20.04 LTS (EOL 2025-04) (our EOL forced by Python 3.8 is 2024-10-14)
+    "ubuntu:jammy",  # 22.04 LTS (EOL 2027-04) (our EOL forced by Python 3.10 is 2026-10-04)
+    "ubuntu:kinetic",  # 22.10 (EOL 2023-07-20) (our EOL forced by Python 3.10 is 2026-10-04)
+    "ubuntu:lunar",  # 23.04 (EOL 2024-01) (our EOL forced by Python 3.11 is 2027-10-24)
 )
 
 DESC = """\