Postgres misses readline

Hello group,

I had postgres running fine for about a year on my local workstation
for testing purposes. After I did not use it some time and then needed
it again, running `$ postmaster` gives me the following error:

dyld: Library not loaded: /opt/local/lib/libreadline.5.0.dylib
Referenced from: /opt/local/bin/postmaster
Reason: image not found
Trace/BPT tra

I updated readline to 5.1. How can I tell postgres to use that instead?
I am using Postgresql 7.4 installed via DarwinPorts on Mac OS 10.4
Tiger. Googling and scanning the manual did not help me.

Thanks in advance,
-justin