diff -Nru ifenslave-2.6-1.1.0/debian/changelog ifenslave-2.6-1.1.0/debian/changelog
--- ifenslave-2.6-1.1.0/debian/changelog	2010-06-11 21:43:10.000000000 +0200
+++ ifenslave-2.6-1.1.0/debian/changelog	2011-05-16 18:37:38.000000000 +0200
@@ -1,3 +1,11 @@
+ifenslave-2.6 (1.1.0-15ubuntu2.11.04.1) natty-proposed; urgency=low
+
+  * Check for previous version to be not set (on fresh install) when
+    comparing versions in postinst.
+    LP: #714904
+
+ -- Stefan Bader <stefan.bader@canonical.com>  Mon, 16 May 2011 16:34:07 +0000
+
 ifenslave-2.6 (1.1.0-15ubuntu2) maverick; urgency=low
 
   * Adjust README.Debian to be consistent with the examples, not advising
diff -Nru ifenslave-2.6-1.1.0/debian/ifenslave-2.6.postinst ifenslave-2.6-1.1.0/debian/ifenslave-2.6.postinst
--- ifenslave-2.6-1.1.0/debian/ifenslave-2.6.postinst	2010-02-04 03:21:26.000000000 +0100
+++ ifenslave-2.6-1.1.0/debian/ifenslave-2.6.postinst	2011-05-16 18:09:13.000000000 +0200
@@ -16,7 +16,7 @@
 
 case "$1" in
 configure)
-        if dpkg --compare-versions "$2" le "1.1.0-6"; then
+	if [ -n "$2" ] && dpkg --compare-versions "$2" le "1.1.0-6"; then
                 mv_conffile "/etc/network/if-up.d/ifenslave" "/etc/network/if-pre-up.d/ifenslave"
                 mv_conffile "/etc/network/if-down.d/ifenslave" "/etc/network/if-post-down.d/ifenslave"
         fi