postmaster segfault when using SELECT on a table

Hello,

I have a smallish postgres database that segfaults everytime when I try to
access a certain row in a certain column.

xxx=# select file_id from dbfiles offset 632531 limit 1;
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.

file_id is a varchar(40).

The database is a selfcompiled 8.2.6 on a x86_64 linux 2.6 machine
that was running well for about 8 months before it started exhibiting the
problem a couple days ago.
I tried upgrading to 8.2.7 but the problem is still occuring.

I have recompiled the postgres server without -O2 and with -g and have
captured a coredump. Here's a bt and the first section of a bt full.
If you need more information, please don't hesistate to contact me.

Core was generated by `postgres: postgres xxx [local] SELECT '.
Program terminated with signal 11, Segmentation fault.
#0 0x000000000067c01b in pglz_decompress (source=0x2b3ab8060910, dest=0xa57744 "d") at pg_lzcompress.c:678
678 *bp = bp[-off];
(gdb) bt
#0 0x000000000067c01b in pglz_decompress (source=0x2b3ab8060910, dest=0xa57744 "d") at pg_lzcompress.c:678
#1 0x00000000004613b6 in heap_tuple_untoast_attr (attr=0x2b3ab8060910) at tuptoaster.c:128
#2 0x00000000006a3a19 in pg_detoast_datum (datum=0x2b3ab8060910) at fmgr.c:1973
#3 0x00000000004423d0 in printtup (slot=0xa3ff78, self=0xa3de00) at printtup.c:317
#4 0x000000000053d184 in ExecSelect (slot=0xa3ff78, dest=0xa3de00, estate=0xa3fe00) at execMain.c:1310
#5 0x000000000053cfea in ExecutePlan (estate=0xa3fe00, planstate=0xa40120, operation=CMD_SELECT, numberTuples=0, direction=ForwardScanDirection, dest=0xa3de00) at execMain.c:1236
#6 0x000000000053b9aa in ExecutorRun (queryDesc=0xa335d0, direction=ForwardScanDirection, count=0) at execMain.c:241
#7 0x00000000005f9f4c in PortalRunSelect (portal=0xa4b6c0, forward=1 '\001', count=0, dest=0xa3de00) at pquery.c:831
#8 0x00000000005f9bc3 in PortalRun (portal=0xa4b6c0, count=9223372036854775807, dest=0xa3de00, altdest=0xa3de00, completionTag=0x7fff01602ac0 "") at pquery.c:656
#9 0x00000000005f4737 in exec_simple_query (query_string=0xa05100 "select file_id from dbfiles offset 632531 limit 1;") at postgres.c:939
#10 0x00000000005f8376 in PostgresMain (argc=4, argv=0x9672c8, username=0x967290 "postgres") at postgres.c:3424
#11 0x00000000005c4318 in BackendRun (port=0x9634d0) at postmaster.c:2934
#12 0x00000000005c38c5 in BackendStartup (port=0x9634d0) at postmaster.c:2561
#13 0x00000000005c154a in ServerLoop () at postmaster.c:1214
#14 0x00000000005c0f70 in PostmasterMain (argc=3, argv=0x946230) at postmaster.c:966
#15 0x0000000000568d76 in main (argc=3, argv=0x946230) at main.c:188
(gdb) bt full
#0 0x000000000067c01b in pglz_decompress (source=0x2b3ab8060910, dest=0xa57744 "d") at pg_lzcompress.c:678
dp = (const unsigned char *) 0x2b3ab80707ea "`"
dend = (const unsigned char *) 0x2b3abff0c03d "6.21.163"
bp = (unsigned char *) 0xa7b000 <Address 0xa7b000 out of bounds>
ctrl = 3 '\003'
ctrlc = 5
len = 5
off = 1633
destsize = 0
__func__ = "pglz_decompress"
--snip

Thanks in advance,
Karsten Desler