Ambigous constructor call with list-initialization

struct A {
    A(int) {}
};

struct B {
    B(A) {}
};

int main() {
    B b({0});
}

The construction of b gives the following errors:

In function 'int main()':
24:9: error: call of overloaded 'B(<brace-enclosed initializer list>)' is ambiguous
24:9: note: candidates are:
11:2: note: B::B(A)
10:8: note: constexpr B::B(const B&)
10:8: note: constexpr B::B(B&&)

I was expecting B::B(A) to be called, why is it ambiguous in this case?