# This state of affairs also persists in glibc2, found
# on linux systems running libc6.
# XXX A Configure test is needed.
-$self->{CCFLAGS} = $Config{ccflags} . ' -DSTRUCT_TM_HASZONE' ;
+
+# Although <unistd.h> is inappropriate in general for SunOS, we need it
+# in POSIX.xs to get the correct prototype for ttyname().
+
+$self->{CCFLAGS} = $Config{ccflags} . ' -DSTRUCT_TM_HASZONE -DI_UNISTD' ;