Compatibility issue with vagrant >0.9.0 ?

I've got everything working more or less correctly for other (test) VMs, but when I try to vagrant up in this project I get:

You are using a feature that has been removed in this version. Explanation:

`config.vm.customize` now takes an array of arguments to send to
`VBoxManage` instead of having a block which gets a virtual machine
object. Example of the new usage:

config.vm.customize ["modifyvm", :id, "--memory", "1024"]

The above will run `VBoxManage modifyvm 1234 --memory 1024` where
"1234" is the ID of your current virtual machine. Anything you could
do before is certainly still possible with `VBoxManage` as well.

Note that this error message will not appear in the next version of Vagrant.

There is a config.vm.customize somewhere in the vagrantfile. Is it possible that the vagrantfile needs to be adapted for newer versions of vagrant? If not, any idea how I can fix it?