diff --git a/docs/installation.rst b/docs/installation.rst
index bb39f9d..fb239fc 100644
--- a/docs/installation.rst
+++ b/docs/installation.rst
@@ -11,8 +11,9 @@ The following packages are user-contributed and were up-to-date at the time of
 writing:
 
 - `ArchLinux (AUR) <https://aur.archlinux.org/packages/vdirsyncer>`_
-- `Ubuntu and Debian <https://packagecloud.io/pimutils/vdirsyncer/install>`_
-  (packages also exist in the official repositories but may be out of date)
+- `Ubuntu and Debian, x86_64-only
+  <https://packagecloud.io/pimutils/vdirsyncer/install>`_ (packages also exist
+  in the official repositories but may be out of date)
 - `GNU Guix <https://www.gnu.org/software/guix/package-list.html#vdirsyncer>`_
 - `OS X (homebrew) <http://braumeister.org/formula/vdirsyncer>`_
 - `BSD (pkgsrc) <http://pkgsrc.se/time/py-vdirsyncer>`_