why does this end in a BAD_ACCESS?

gistfile1.m

@implementation SBAppDelegate {
    __weak NSNumber *aNumber;
    NSNumber *anotherNumber;
}

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    NSNumber *myNumber = [NSNumber numberWithInt:2];
    self->anotherNumber = myNumber;
    self->aNumber = myNumber;
}