bad_weak_ptr when shared_from this() after i already make shared_ptr?

I have already create a shared_ptr,but why i still get the bad_weak_ptr runtime error?Does any one know the reason and how can i do for that?

class base:enable_shared_from_this<base> {
public:
    virtual void wtf() { shared_from_this(); };//bad_weak_ptr here
};
class c1 :public base {};
using basep = shared_ptr<base>;
void main() {
    basep bp = make_shared<c1>();//shared_ptr here
    bp->wtf();
}