Vagrant ifup eth1 failing (duplicate interface)

I am trying to build a vagrant box from a VirtualBox machine. When I give vagrant up, I get an error saying

The following SSH command responded with a non-zero exit status.
Vagrant assumes that this means the command failed!

/sbin/ifup eth1

If I try to run the command manually, I get

/etc/network/interfaces:17: duplicate interface
ifup: couldn't read interfaces file "/etc/network/interfaces"

The network-related part of the vagrantfile is

config.vm.network :hostonly, "192.168.56.11"

(if I disable this line and use only a NAT interface, things work, but I would like both a NAT and a host-only network connection)

The contents of /etc/network/interfaces is

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug eth0
iface eth0 inet dhcp

allow-hotplug eth1
iface eth1 inet dhcp
#VAGRANT-BEGIN
# The contents below are automatically generated by Vagrant. Do not modify.
auto eth1
iface eth1 inet static
      address 192.168.56.11
      netmask 255.255.255.0
#VAGRANT-END

I tried commenting out the iface eth1 inet dhcp before packaging the machine, but it didn't have any effect (the line was not commented out on the vagrant box).