Should I always release self when there is a failure inside init, or should I only do so if I have initialized instance variables first?

To put it another way, is this pattern valid? Is there a time when I shouldn't release self inside an init method, or should I assume that if the control flow enters init, self has at least a retain count of 1?

- (id)init
{
 if ((self = [super init]) == nil)
 {
  [self release];
  return nil;
 }

 //do some init stuff
 if (somethingFailed)
 {
  [self release];
  return nil;
 }
 return self;
}