Is there a way to get the negation of if a function exists for an object?

To determine if a function exists for a function, you can use the following:

template <typename...Ts>
using void_t = void;

void fn(int);

struct X {};

template <typename T, typename = void_t<decltype(fn(std::declval<T>()))>>
void fn2(T) { }

void test() {
  fn2(int(1)); // works
  //fn2(X()); // doesn't work
}

Now, is there a way of detecting if the fn(T) doesn't exist for type T?

Example:

void test2() {
  //fn2(int(1)); // doesn't work
  fn2(X()); // works
}