How does the spell Longstrider interact with Gaseous Form?

The 3rd-level spell Gaseous Form states that you have a flying speed of 10 feet.

If you cast Longstrider beforehand, does this in practice mean that your flying speed is effectively now 20 feet?

I can’t see why not, but I just wanted to confirm how these two spells interact first – as this could make quite a nice escape tactic.