Diffuse Pass with Alha channel?

I’m not sure if I’m missing something, but when I rendered out a Diffuse Pass (through the compositor), there doesn’t seem to be an alpha channel. When I render out the default Image pass, it has an alpha, but not the diffuse.
Can I render out the Diffuse with an alpha channel?
Thanks in advance.

You may have to enable the Alpha under the Shading panel. Change it from Sky to Transparent and re-render your pass.

No, but you can just pull the alpha channel from the combined pass.

Or use an object ID or any kind of mask. You can use “separate RGBA” and “combine RGBA” to add an alpha to an image (Blender equivalent of Nuke’s “shuffle” node).

For Cycles you have to enable Transparent under the Film rollout as well.