diff --git a/man/pam_systemd.xml b/man/pam_systemd.xml
index cc80205685..3e106ea69b 100644
--- a/man/pam_systemd.xml
+++ b/man/pam_systemd.xml
@@ -273,8 +273,13 @@
                                 <varname>$XDG_CURRENT_DESKTOP</varname>,
                                 as defined by the <ulink
                                 url="http://standards.freedesktop.org/desktop-entry-spec/latest/">Desktop
-                                Entry
-                                Specification</ulink>. See
+                                Entry Specification</ulink>. (However,
+                                note that
+                                <varname>$XDG_SESSION_DESKTOP</varname>
+                                only takes a single item, and not a
+                                colon-separated list like
+                                <varname>$XDG_CURRENT_DESKTOP</varname>.)
+                                See
                                 <citerefentry><refentrytitle>sd_session_get_desktop</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                 for more details.</para></listitem>
                         </varlistentry>