mem_fn: unresolved overloaded function type

mem_fn.cpp

// g++ -std=c++14 -c mem_fn.cpp
//
// error: no matching function for call to ‘mem_fn(<unresolved overloaded function type>)’
#include <vector>
#include <functional>
#include <algorithm>

using namespace std;

struct A {
    int& getAttribute();
    const int& getAttribute() const;
};

vector<int> foo(const vector<A>& as) {
    vector<int> is;
    transform(as.begin(), as.end(), back_inserter(is), mem_fn(&A::getAttribute));
    return is;
}