diff --git a/debian/changelog b/debian/changelog
index c0141c6..9062eab 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,11 @@
+lubuntu-default-settings (0.21) UNRELEASED; urgency=low
+
+  * debian/postinst,debian/postrm: set lubuntu as the default session and
+    lightdm-gtk-greeter as the default greeter if they aren't set already.
+    Remove them on uninstall. (thanks Didier and Lionel !)
+
+ -- Julien Lavergne <gilir@ubuntu.com>  Tue, 16 Aug 2011 01:11:02 +0200
+
 lubuntu-default-settings (0.20) oneiric; urgency=low
 
   [ Jonathan Marsden ]
diff --git a/debian/postinst b/debian/postinst
index 40a0d8e..d51147d 100644
--- a/debian/postinst
+++ b/debian/postinst
@@ -15,6 +15,13 @@ if [ "$1" = configure ]; then
     lxdm.conf /etc/xdg/lubuntu/lxdm/lxdm.conf 60 
 fi
 
+if [ "$1" = configure|upgrade ]; then
+  if [ -x /usr/lib/lightdm/lightdm-set-defaults ] ; then
+    /usr/lib/lightdm/lightdm-set-defaults --keep-old --session=lubuntu || true
+    /usr/lib/lightdm/lightdm-set-defaults --keep-old --greeter=lightdm-gtk-greeter || true
+  fi
+fi
+
 if dpkg-maintscript-helper supports mv_conffile 2>/dev/null; then
     dpkg-maintscript-helper mv_conffile /etc/xdg/pcmanfm/lubuntu.conf /etc/xdg/pcmanfm/lubuntu/pcmanfm.conf 0.15 -- "$@"
 fi
diff --git a/debian/postrm b/debian/postrm
index 390e22c..738e214 100644
--- a/debian/postrm
+++ b/debian/postrm
@@ -6,5 +6,15 @@ if dpkg-maintscript-helper supports mv_conffile 2>/dev/null; then
     dpkg-maintscript-helper mv_conffile /etc/xdg/pcmanfm/lubuntu.conf /etc/xdg/pcmanfm/lubuntu/pcmanfm.conf 0.15 -- "$@"
 fi
 
+case "$1" in
+  remove|purge)
+    if [ -x /usr/lib/lightdm/lightdm-set-defaults ] ; then
+      /usr/lib/lightdm/lightdm-set-defaults --remove --session=lubuntu || true
+      /usr/lib/lightdm/lightdm-set-defaults --remove --greeter=lightdm-gtk-greeter || true
+    fi
+    ;;
+esac
+
+
 #DEBHELPER#
 exit 0