Wrong warning about data volumes capacity

I see the following warning trying to run nodetool upgradesstables

WARN  16:09:24 Only 34988 MB free across all data volumes. Consider adding more capacity to your cluster or removing obsolete snapshots

This warning is wrong because the wrong storage device capacity gets tested.

All my cassandra data paths are subdirectories of /data mount point which has enough of space:

$ df -h /data
Filesystem      Size  Used Avail Mounted on
.................     1.2T 200G  1T  /data

However what Warning reports is a OS mount which has nothing to do with Cassandra configuration:

df -h /
Filesystem      Size  Used Avail Use% Mounted on
............        40G  5.7G   35G  15% /

I see this error running Cassandra 3.0.22