Can't install postgresql96-client with PREFIX

[webern]

when I run "make PREFIX=/usr/local/pgsql96 install", it return many lines looks like below:

.....
pkg-static: Unable to access file /usr/ports/databases/postgresql96-client/work/stage/usr/local/pgsql96/include/postgresql/server/catalog/pg_largeobject_metadata.h: No such file or directory
pkg-static: Unable to access file /usr/ports/databases/postgresql96-client/work/stage/usr/local/pgsql96/include/postgresql/server/catalog/pg_namespace.h: No such file or directory
pkg-static: Unable to access file /usr/ports/databases/postgresql96-client/work/stage/usr/local/pgsql96/include/postgresql/server/catalog/pg_opclass.h: No such file or directory
pkg-static: Unable to access file /usr/ports/databases/postgresql96-client/work/stage/usr/local/pgsql96/include/postgresql/server/catalog/pg_operator.h: No such file or directory
pkg-static: Unable to access file /usr/ports/databases/postgresql96-client/work/stage/usr/local/pgsql96/include/postgresql/server/catalog/pg_operator_fn.h: No such file or directory
pkg-static: Unable to access file /usr/ports/databases/postgresql96-client/work/stage/usr/local/pgsql96/include/postgresql/server/catalog/pg_opfamily.h: No such file or directory
.....

I found that the path "/usr/ports/databases/postgresql96-client/work/stage/usr/local/pgsql96/include/postgresql/server" is wrong, the right path is "/usr/ports/databases/postgresql96-client/work/stage/usr/local/pgsql96/include/server", how to fix it?