Can't exec "dpkg-architecture" … on Ubuntu 11.10

Ran into a puzzling problem today setting up PostgreSQL 9.1. After creating a user and logging in, I was greeted with:

$ psql postgres brad
Can't exec "dpkg-architecture": No such file or directory at /usr/bin/psql line 103.
Use of uninitialized value $multiarch in scalar chomp at /usr/bin/psql line 104.
psql (9.1.3)
Type "help" for help.

postgres=#

It seems the package dpkg-dev wasn't installed for some reason…

Easy fix:

sudo apt-get install dpkg-dev