I'm trying to export to HTML a file with this snippet of text:

<<
call_function 0; store 1 (a)
>>

Doing so gives me the error: *Variable "store" must be assigned a default
value*

This goes away if I remove the underscore. I've tried using #+OPTIONS: ^:{}
to address this, but it doesn't have any effect, nor does #+OPTIONS: ^:nil

Org is version 8.2.10. Emacs is 25.0.50.1.

What seems to be the matter here and how can I fix it?