diff --git a/rpm_spec/core-dom0.spec b/rpm_spec/core-dom0.spec
index 58ba4e1d..80e7d3d7 100644
--- a/rpm_spec/core-dom0.spec
+++ b/rpm_spec/core-dom0.spec
@@ -114,6 +114,9 @@ sed -i 's/\/block /\/block.qubes /' /etc/udev/rules.d/xen-backend.rules
 
 %post
 
+if ! grep -q ^no-auto-default.*=.*FE:FF:FF:FF:FF:FF /etc/NetworkManager/nm-system-settings.conf ; then
+	echo no-auto-default=FE:FF:FF:FF:FF:FF >> /etc/NetworkManager/nm-system-settings.conf
+fi
 if [ -e /etc/yum.repos.d/qubes-r1-dom0.repo ]; then
 # we want the user to use the repo that comes with qubes-code-dom0 packages instead
 rm -f /etc/yum.repos.d/qubes-r1-dom0.repo
diff --git a/rpm_spec/core-netvm.spec b/rpm_spec/core-netvm.spec
index 88255aee..1717b6b1 100644
--- a/rpm_spec/core-netvm.spec
+++ b/rpm_spec/core-netvm.spec
@@ -80,6 +80,10 @@ cp /var/lib/qubes/serial.conf /etc/init/serial.conf
 
 %post
 
+if ! grep -q ^no-auto-default.*=.*FE:FF:FF:FF:FF:FF /etc/NetworkManager/nm-system-settings.conf ; then
+	echo no-auto-default=FE:FF:FF:FF:FF:FF >> /etc/NetworkManager/nm-system-settings.conf
+fi
+
 if [ "$1" !=  1 ] ; then
 # do this whole %post thing only when updating for the first time...
 exit 0