diff --git a/README.adoc b/README.adoc
index a31b524..8e76970 100644
--- a/README.adoc
+++ b/README.adoc
@@ -12291,6 +12291,18 @@ xdg-open "$(./getvar --arch aarch64 --gem5-build-id ruby gem5_build_build_dir)/A
 
 A minimized ruby config which was not merged upstream can be found for study at: https://gem5-review.googlesource.com/c/public/gem5/+/13599/1
 
+==== gem5 Python 3 build
+
+Python 3 support was mostly added in 2019 Q3 at arounda347a1a68b8a6e370334be3a1d2d66675891e0f1 but remained buggy for some time afterwards.
+
+In an Ubuntu 18.04 host where `python` is `python2` by default, build with Python 3 instead with:
+
+....
+./build-gem5 --gem5-build-id python3 -- PYTHON_CONFIG=python3-config
+....
+
+Python 3 is then automatically used when running if you use that build.
+
 === gem5 ARM platforms
 
 The gem5 platform is selectable with the `--machine` option, which is named after the analogous QEMU `-machine` option, and which sets the `--machine-type`.