Is MANA SPELLUP subject to armor hindrance?

My ranger just got the ability and now I'm paranoid I'll waste my one daily use because I forgot to remove my brig...

Starchitin

A severed gnomish hand crawls in on its fingertips and makes a rude gesture before quickly decaying and rotting into dust. A gust of wind quickly scatters the dust.

It is subject, but you don't lose it if the hindrance stops it.