8.3.6 build error on Debian Lenny

Hi - I'm trying to build 8.3.6 on a box recently upgraded from Sarge
to Lenny and I get the following error during compile:

make[4]: Entering directory
`/backup/source/db/postgresql-8.3.6/src/backend/utils/adt' gcc -O2
-Wall -Wmissing-prototypes -Wpointer-arith -Winline
-Wdeclaration-after-statement -Wendif-labels -fno-strict-aliasing
-fwrapv -I../../../../src/include -D_GNU_SOURCE -I/usr/local/lib -c
-o geo_ops.o geo_ops.c /usr/lib/gcc/i486-linux-gnu/4.3.2/cc1: symbol
lookup error: /usr/lib/libmpfr.so.1: undefined symbol:
__gmp_get_memory_functions

./configure --prefix=/usr/local/pgsql-8.3.6 --with-python
--with-perl --with-openssl --with-libraries=/usr/local/lib
--with-includes=/usr/local/lib

dpkg -S /usr/lib/libmpfr.so.1
libmpfr1ldbl: /usr/lib/libmpfr.so.1

Any ideas? Google isn't telling me much that I can understand. :(

Thanks,

Josh