Function signatures in export file (*.h) using bool return type

I have a file:

// mylib.c// -------#include <stdbool.h>bool is_zero(int n){  return (n == 0);}

And a file detailing what functions to export:

// mylib.h// -------bool is_zero(int n);

When I compile, I get "mylib.o: error: unkown type name 'bool'"

Am I missing something? Do I need to do something special when my exported functions have a signature that requires an exported type?