Sugarcube 2.21 Macro <<set $variable>> having subtraction problems

Question

Very basic question, but I have been struggling to figure out why this is not working. I am attempting to check that my variable is being properly subtracted from, but I continue to get the error:

Error: <<set>>: bad evaluation: Unexpected token -=

 Here is the full code I am working with right now:

<<set $lohiusmood to 16>>

<<if $lohiusmood lt 17>> ^I Will Be Fine.^ Lohius repeats, reclasping his hands behind his back, giving you a flat look. ^There Is No Need For You To Concern Yourself.^

[[=>->Interrogation Start]] 
<<set $lohiusmood to -= 7>> <</if>>

$lohiusmood

I cannot figure out why it is saying that the -= is an unexpected token. I have not had this problem when doing addition with +=. 

Edit: Nevermind, I am also having this problem with +=.

Answer 1

Nevermind, posted the question then literally took one more look at my code and realized I had the "to" in there. Removed it and it started working.