Steam currently provides binaries for amd64 and i386 architectures only. Debian and Ubuntu support more than these two architectures and for some usecases it makes sense to add non-x86 architectures to dpkg. For example, when doing cross-compilation for ARM, people might want to add "armel" or "armhf" to dpkg.

However, since Steam is i386 and amd64 only, enabling dpkg for non-x86 architectures on systems where Steam is installed, will result in an error when running "apt-get update". Luckily, this can be fixed very easily by specifying the supported architectures in sources.list.d/steam.iist.

How to reproduce:

root@z6:~# dpkg --add-architecture armhf
root@z6:~# apt-get update
(...)
W: Failed to fetch http://repo.steampowered.com/steam/dists/precise/InRelease Unable to find expected entry 'steam/binary-armhf/Packages' in Release file (Wrong sources.list entry or malformed file)

Patch to fix the issue:

--- steam.list.old 2013-12-11 16:50:35.183329854 +0100
+++ steam.list 2013-12-11 16:51:02.631330732 +0100
@@ -1,2 +1,2 @@
-deb http://repo.steampowered.com/steam/ precise steam
-deb-src http://repo.steampowered.com/steam/ precise steam
+deb [arch=amd64,i386] http://repo.steampowered.com/steam/ precise steam
+deb-src [arch=amd64,i386] http://repo.steampowered.com/steam/ precise steam

Cheers,

Adrian