AVR erwacht nicht mehr aus Sleepmode

int main(void)

{

  unsigned char i;

  sei();

  DDRD  &= ~(1<<PD3);  // configure PD2 as input

  MCUCR |= (1<<ISC10);  // Interrupt is generated on any logic 

  GICR |= (1<<INT1);  // enable external interrupt 6    

  for (;;)

  {

    unsigned char i;

    for(i=0;i<10;i++)

    {

      PORTC |= (1<<PC2);

      _delay_ms(50);

      PORTC &= ~(1<<PC2);

      _delay_ms(50);

    }

    set_sleep_mode(SLEEP_MODE_PWR_DOWN);

      _delay_ms(500);

      sleep_mode();

  }

}

ISR(INT1_vect)

{

  PORTC |= (1<<PC2);

}