This doesn't seem correct. OS X defines `key_t` as `__int32_t`, which in turn is defined as `int` (see `/usr/include/sys/_types/_key_t.h` and `/usr/include/i386/_types.h`). It doesn't fundamentally change the argument, though. Note that `IPC_PRIVATE` is `(key_t) 0` and `ftok()` is defined to return `(key_t)-1` on error: http://pubs.opengroup.org/onlinepubs/007904975/functions/ftok.html