Meteor MCrypt app will not compile on heroku because it's missing libmcrypt4 etc

I am trying to push a simple meteor application to heroku that uses the mcrypt package.

It works perfect on my local machine as i used brew to install mcrypt which included all of the dev libs.

However when pushing to heroku, mcrypt cannot compile. The error is:

In file included from ../src/mcrypt.cc:3:0:
../src/mcrypt.h:10:20: fatal error: mcrypt.h: No such file or directory
#include 
^
compilation terminated.
make: *** [Release/obj.target/mcrypt/src/mcrypt.o] Error 1

Does anyone have any ideas how I can make this work? thanks