constexpr doesn't seem to work

I'm using Visual Studio 2013 + CTP.

I have defined the following function:

constexpr DWORD const_getHash(const char *str, DWORD curHash = 0) {
    return !*str ? curHash : const_getHash(str + 1, 
        (curHash >> 13 | curHash << (32 - 13)) + (*str >= 'a' ? *str - 32 : *str));
}

which I use like this:

DWORD hash = const_getHash("ok");

The compiler doesn't issue any warnings but by looking at the "disassembly" I can tell that const_getHash() is executed at runtime.

What's wrong?