Weird undefined symbols of static constants inside a struct/class

Either I'm very tired or something weird is happening that I'm not aware of, because the code below is resulting in undefined symbols for Foo::A and Foo::B when linking. This is minimized as much as I could from a larger project, but shows the essence of what I'm looking at.

#include <algorithm>

struct Foo
{
    static const int A = 1;
    static const int B = 2;
};

int main()
{
    return std::min(Foo::A, Foo::B);
}

Without the std::min function template it works fine, i.e. just return Foo::A. Also fine is when defining the static ints outside a class/struct (global in this simple case). However, as soon as they're inside like this, the linker cannot find them.

Can someone explain what's happening?