Why does Boost::multiprecision::sqrt(1) return 0?

Boost::multiprecision::sqrt(1) seems to return 0

#include <boost/multiprecision/cpp_int.hpp>

#include <boost/multiprecision/number.hpp>

#include <iostream>



using std::cout;

using std::endl;



int main() {

   namespace mp = boost::multiprecision;

   mp::cpp_int i(1); 

   cout << "i == " << i << endl;

   cout << "mp::sqrt(i) == " << mp::sqrt(i) << endl;

}

Output:

i == 1

mp::sqrt(i) == 0

I expect that sqrt(1) == 1.

I get the same results on coliru and on my local installation with gcc and Boost 1.62. Does this happen to others? Am I missing something or is this a bug?