... Now that you have declared the functions to be exported, you also have to introduce them to Zend. ... This array consecutively contains all functions that are to be made available externally, with the function's name as it should appear in PHP and its name as defined in the C source. ... zend_function_entry firstmod_functions[] = { ZEND_FE(first_module, NULL) {NULL, NULL, NULL} }; You can see that the last entry in the list always has to be {NULL, NULL, NULL} . ... ZEND_FE(name, arg_types) . ...