AVR Freaks

I think that this should be toggling PORTB's first pin, however when I debug it the event is never fired.  It seems that the program hangs at sei().   If I manually set TOV2 in TIFR2 then the event fires and the breakpoint set in ISR is reached.

#include <avr/io.h>
#include <avr/interrupt.h>

int main(void) {
    DDRD = 0b00000001;
    cli();

    TCCR2A |= (1 << CS20);
    TIMSK2 |= (1 << TOIE2);

    sei();
    while (1) {
    }
}

The I/O window had the correct bit set.

I thought that it might be that the while loop was getting optimised away by the compiler so I tried adding a write to the PORTB register so that it was doing something important. 

while (1) {
    PORTD++;
}

That seems to be preventing the while loop from vanishing but the interrupt at TOV2 still isn't firing.