Attiny13 INT0 Logical Change Problem

#include <avr/interrupt.h>

#include <avr/io.h>

#include <util/delay.h>

ISR (INT0_vect) {

  if (PINB & (1<<PINB1)) {

    PORTB &= ~(PB5);

    PORTB |= (1<<PB4);

  } else {

    PORTB &= ~(PB4);

    PORTB |= (1<<PB5);

  }

}

int main(void) {

  // Outputs

  DDRB |= (1<<PB4);

  DDRB |= (1<<PB5);

  // Inputs

  DDRB &= ~(1<<PB1);

  PORTB |= (1<<PB1);

  // Start Sequenze. Only for test

  PORTB |= (1<<PB4);

  _delay_ms(200);

  PORTB &= ~(1<<PB4);

  _delay_ms(400);

  PORTB |= (1<<PB4);

  _delay_ms(200);

  PORTB &= ~(1<<PB4);

  // Interrupts

  // INT0 = Pin Logical Change

  MCUCR |= (1<<ISC00);

  // INT0 = enable

  GIMSK |= (1<<INT0);

  // Enable Interrupts

  sei();

  while(1) {

  }

}