Active MQ Shared File System Master Slave with Elastic File System

I'm setting up Active MQ in production with a shared file system master/slave configuration (KahaDB). I've set everything up and mounted the EFS on both EC2 instances.

When I check the disk free stats I get 8 exabytes for the shared file system:

$ df -h
eu-west-1a.***.efs.eu-west-1.amazonaws.com:/  8.0E     0  8.0E   0% /mnt/efs

Unfortunately, ActiveMQ cannot interpret this number:

Store limit is 102400 mb (current store usage is 0 mb). The data directory: /mnt/efs/kahadb only has -8796093022208 mb of usable space - resetting to maximum available disk space: -8796093022207 mb
Store limit is -8796093022207 mb, whilst the max journal file size for the store is: 32 mb, the store will not accept any data when used.

Which currently prevents its use.

Is there a way to force the OS to report a sensible size for the file system or turn off the FS checking in Active MQ?