Trying to build hylafax produces the following:

===>  Validating dependencies for tkhylafax-3.1
>> Checksum OK for tkhylafax-3.1.tar.gz.
===>  Extracting for tkhylafax-3.1
===>  tkhylafax-3.1 depends on package: hylafax-4.1b2
===>  Verifying install for ../../comms/hylafax
===>  Building for hylafax-4.1b2
= port
= regex
= util
/usr/bin/g++      -I/usr/include  -D__ANSI_CPP__ -I. -I.. -I.././regex -I.././util  -I.././util -I/usr/pkg/include -g -O  -c Dispatcher.c++
Sys.h: In function `static void Sys::waitpid(pid_t)':
In file included from Dispatcher.c++:27:
Sys.h:113: `NULL' undeclared (first use this function)
Sys.h:113: (Each undeclared identifier is reported only once
Sys.h:113: for each function it appears in.)
*** Error code 1

Stop.
*** Error code 1

Stop.
*** Error code 1

Any ideas on how to fix this?

Brad