Sometimes it is necessary to work around bugs in software included with older versions of FreeBSD.
Some versions of make(1) were broken on at least 4.8 and 5.0 with respect to handling comparisons based on OSVERSION. This would often lead to failures during make describe (and thus, the overall ports make index). The workaround is to enclose the conditional comparison in spaces, e.g.:
if ( ${OSVERSION} > 500023 )
Be aware that test-installing a port on 4.9 or 5.2 will not detect this problem.