Middleman build not compiling .md into .html, but only on Heroku

I’m using Middleman to push a bunch of documentation for a system I’m working on (in markdown format) to a Heroku app instance. It’s pretty simple, and I’ve got it all working locally, both dynamically (ie by running a local instance of a middleman server) and statically (ie from static files served from a local web server instance after running ‘middleman build’).

The problem is, when I deploy to heroku, the ‘middleman build’ command is only generating stuff in the top level directory, plus asset stuff like fonts, javascripts and stylesheets. It is not generating any of my markdown files, which are all located underneath source/docs/**.

Is there a configuration option that I’m missing from Heroku that would force the creation of the static assets that exist in the source/docs directory?

I’m obviously missing something really simple, but I just can’t get it to work.

Thanks in advance,
M@