1.3beta and SDK 4 compile error - usleep was not declared in this scope

I get one error when trying to build a 1.3beta project with SDK4 - usleep was not declared in this scope.

I'm not proficient with objective C. Anyone know how I can fix this?

usleep is from this method.

/// Asks the operating system to put the process to sleep for at least ms milliseconds
void Platform::sleep(U32 ms)
{
// note: this will overflow if you want to sleep for more than 49 days. just so ye know.
// -Mat Need to fix this
usleep( ms * 1000 );
}