Can't find variable: random

Hi everyone,

Having an odd problem as of late (using Twine 2.1.1)

I have a common expressions:

(set: $variableName to random(0,10))

~or~

(set: $someVariable to $someVariable - random(0,10))

And both throw up this error:

Can’t find variable: random

I’ve used this syntax plenty of times without error, and not I can’t figure out what’s wrong.

Thanks!