Slices and arrays problems?

[Damian]

void testref(ref int[] arr)
{
     arr[0] = 1;
}

void test(int[] arr)
{
     arr[0] = 1;
}

void main()
{
     //int[] buffer1 = new int[4]; // This works
     int[4] buffer1; // This doesn't
     int[4] buffer2;

     testref(buffer1);
     test(buffer2);
	
     assert(buffer1[0] == 1);
     assert(buffer2[0] == 1);
}

I'm not sure why my code doesn't work?? Isn't the buffer just an 
array with a fixed length? DMD is telling me 'buffer1 is not an 
lvalue'. The non ref version works fine?!