hrStorageSize overflow on large filesystems

Platform is a Solaris 10 box with a very large filesystem:

# df -h /export
Filesystem size used avail capacity Mounted on
Export 1.2T 3.8G 1.1T 1% /export
# df -k /export
Filesystem kbytes used avail capacity Mounted on
Export 1261338624 4032640 1139000439 1% /export

Agent is Net-SNMP 5.4. A walk of hrStorage for this filesystem looks like
this:

HOST-RESOURCES-MIB::hrStorageIndex.36 = INTEGER: 36
HOST-RESOURCES-MIB::hrStorageType.36 = OID: HOST-RESOURCES-TYPES::hrStorageFixedDisk
HOST-RESOURCES-MIB::hrStorageDescr.36 = STRING: "/export"
HOST-RESOURCES-MIB::hrStorageAllocationUnits.36 = INTEGER: 512 Bytes
HOST-RESOURCES-MIB::hrStorageSize.36 = INTEGER: -2008937171
HOST-RESOURCES-MIB::hrStorageUsed.36 = INTEGER: 8065273
HOST-RESOURCES-MIB::hrStorageAllocationFailures.36 = Counter32: 0

What's with the negative numbers in hrStorageSize? Wait a minute, the MIB
for hrStorageSize says:

 SYNTAX     Integer32 \(0..2147483647\)

and I'd expect the val to be: 2522677248 (size in kbytes * 2 = size in 512b blocks)

so this is an overflow of Integer32? Why is disk size a signed value?