How do I generate two independent discretized Brownian paths in C++?

The following code generates a discretized Brownian path:

std::vector<double> brownian_path(double t, std::size_t n)
{
    std::random_device rd;
    std::mt19937 gen(rd());
    std::normal_distribution<> dis;

    std::vector<double> bm(n + 1);
    auto const sqrt_dt = std::sqrt(t / n);

    for (std::size_t i = 1; i <= n; ++i)
        bm[i] = bm[i - 1] + sqrt_dt * dis(gen);
    return bm;
}

However, it yields the same Brownian path, each time it's called. So, what do I need to do, to generate a new Brownian path at each call?