C error: initializer element is not constant

I have some code that looks like this.


typedef struct {
   void *ptr;
} Foo;

static const size_t a = 1024;
static const size_t b = 1024;
static const size_t c = 1024;
static const size_t d = a * b + c * sizeof(Foo);

On the line declaring and initializing "d", I get the error "error: initializer element is not constant". Now, maybe I'm missing something, but aren't all of the operands there constant, therefore known at compile-time, therefore usable when initializing a constant?

What kind of compiler is that?
sizeof() is constant.