Proftpd with postgres support

I’d like to install the proftpd server with postgres support.
I compiled postgres the standard way (into /usr/local/postgres) and want proftpd to use its databases for user authentification.

I followed the guidelines in https://www.afp548.com/Articles/Jaguar/proftpd.html and run the configure script as follows:

./configure –prefix=/usr/local –with-modules=mod_sql:mod_sql_postgres –with-includes=/usr/local/include –with-libraries=/usr/local/pqsql/lib

With these options, I get the following error:

gcc -DDARWIN6_4 -DDARWIN6 -I.. -I../include -I/usr/local/include -O2 -Wall -Wno-long-double -c mod_sql_postgres.c
mod_sql_postgres.c:38: header file ‘pgsql/libpq-fe.h’ not found
mod_sql_postgres.c:65: undefined type, found `PGconn’
mod_sql_postgres.c:66: undefined type, found `PGresult’
mod_sql_postgres.c:237: undefined type, found `PGresult’
cpp-precomp: warning: errors during smart preprocessing, retrying in basic mode

Can anybody help me?

Thanks a lot,
Dennis