CVS psql segfault

I'm getting a crash if I run 'psql' with no arguments:

Program received signal SIGSEGV, Segmentation fault.
0x4207a991 in strncpy () from /lib/tls/libc.so.6
(gdb) bt
#0  0x4207a991 in strncpy () from /lib/tls/libc.so.6
#1  0x08050f54 in get_prompt (status=PROMPT_READY) at prompt.c:111
#2  0x0804ec68 in MainLoop (source=0x4212fcc0) at mainloop.c:178
#3  0x0805061a in main (argc=1, argv=0xbffff7a4) at startup.c:301
#4  0x420156a4 in __libc_start_main () from /lib/tls/libc.so.6
(gdb) up
#1  0x08050f54 in get_prompt (status=PROMPT_READY) at prompt.c:111
111                                                     strncpy(buf,
PQdb(pset.db), MAX_PROMPT_SIZE);
(gdb) print PQdb(pset.db)
$1 = 0x0

If I give a database name on the command line, then it works fine; its
just the default which fails.

Bradley