Undefined reference to pthread CLion

I'm trying to run this simple thread c++ program in CLion

> #include <iostream>
> #include <thread>
> 
> using namespace std;
> 
> 
> //Start of the thread t1
> void hello() {
>     cout << "Hello,concurrent world!" << endl; }
> 
> 
> 
> int main() {
>     thread t1(hello);     // spawn new thread that calls hello()
> 
>     cout << "Concurrency has started!" << endl;
>     t1.join();            
> 
>     cout << "Concurrency completed!";
> 
>     return 0; }
> 

My problem is that there's an error of undefined reference to pthread, and I don't undestand what I'm doing wrong... please notice that I'm doing this on CLion.