Help calling optional functions in an apache module

Hello all, I'm writing a PHP module that's closely tied to a custom Apache 2 module. My goal is to allow the PHP module to run with reduced functionality if the Apache module isn't loaded. It seems that using Apache's optional function interface is the way to go, but I can't seem to make it work. I have what I think are all the correct headers in place, but I keep getting these compile errors: /projects/phparm/trunk/phparm.c:86: error: `arm_application_get_ptr' undeclared (first use in this function) /projects/phparm/trunk/phparm.c:86: error: `apr_OFN_arm_application_get_t' undeclared (first use in this function) Although the correct header file is in place to get optional functions, all the definitions are ignored. Is there a -D directive I need to get this to work? Am I missing something fundamental? Do you need more info? Please help! TIA, Dave