Memory Issue with array_agg?

When using array_agg on a large table, memory usage seems to spike up until
Postgres crashes with the following error:

2013-08-17 18:41:02 UTC [2716]: [2] WARNING: terminating connection because
of crash of another server process
2013-08-17 18:41:02 UTC [2716]: [3] DETAIL: The postmaster has commanded
this server process to roll back the current transaction and exit, because
another server process exited abnormally and possibly corrupted shared
memory.
2013-08-17 18:41:02 UTC [2716]: [4] HINT: In a moment you should be able to
reconnect to the database and repeat your command.

I've definitely isolated it down to using array_agg, as when I changed the
query to use string_agg, it worked fine. I also tried using array_agg on a
few different queries, all yielding the same issue. Swapping in string_agg
fixed the issue once more.

This particular table has over 2 million rows and is 1.2 Gigs, and when I
ran the query while viewing htop, the virtual size of the Postgres process
ballooned to 13.9G until crashing.

The version of Postgres I am using is: PostgreSQL 9.2.4 on
x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu/Linaro 4.7.2-2ubuntu1)
4.7.2, 64-bit

Any help would be much appreciated, thanks!

-Robert