[exim] Error compiling Exim on MacOSX

Hi,
I'm compiling Exim on MacOSX (MacBook Intel Core Duo). I've compiled
Berkeley DB and OpenLDAP. When I compile Exim, I get this error:

awk '{ print ($1+1) }' cnumber.h > cnumber.temp
rm -f cnumber.h; mv cnumber.temp cnumber.h
cc version.c
rm -f exim
cc -o exim
/usr/bin/ld: Undefined symbols:
_ber_pvt_opt_on
collect2: ld returned 1 exit status
make[1]: *** [exim] Error 1
make: *** [go] Error 2

What is the problem?

Thanks!

Israel.