Cannot add a decimal when defining messaging costs

When adding a new messaging cost: http://qa-vumi.za.prk-host.net/admin/billing/messagecost/add/

I am not able to enter a decimal. For e.g. Vumi's per message storage cost is .001 which I currently cannot add.

![screen shot 2013-11-18 at 11 34 52 am](https://f.cloud.github.com/assets/1521387/1561741/cb2c077e-5039-11e3-9168-be472bc99c9b.png)