function D2 = constructSymmetricD2(g, order, opSet)
    m = g.size();
    ops = cell(g.D(),1);
    I = cell(g.D(),1);
    for i = 1:g.D()
       lim = {g.x{i}(1), g.x{i}(end)};
       ops{i} = opSet(m(i), lim, order);
       I{i} = speye(m(i));
    end

    switch g.D()
        case 1
            e_r = ops{1}.e_r;
            e_l = ops{1}.e_l;
            Hi = ops{1}.HI;            
            if isequal(opSet,@sbp.D1Upwind)
                B = e_r*e_r' - e_l*e_l';
                Dm = sparse(ops{1}.Dm);
                Dp = sparse(ops{1}.Dp);
                M =  sparse(Dm - Hi*B);
                D2 = @(Viscosity) M*Viscosity*Dp;
            else
                % TODO: Fix Viscosity not being vector
                d1_r = ops{1}.d1_r';
                d1_l = ops{1}.d1_l';
                D2 = @(Viscosity)ops{1}.D2(diag(Viscosity)) + Hi*(Viscosity(1,1)*e_l*d1_l - e_r*Viscosity(end,end)*d1_r);
            end
        case 2
            % TODO: 
            % Currently only implemented for upwind operators.
            % Remove this part once the time-dependent D2 operator is implemented for other opSets
            % or if it is decided that it should only be supported for upwind operators.
            assert(isequal(opSet,@sbp.D1Upwind))
            e_e = kron(ops{1}.e_r,I{2});
            e_w = kron(ops{1}.e_l,I{2});
            Dm_x = kron(ops{1}.Dm,I{2});
            Dp_x  = kron(ops{1}.Dp,I{2});
            H_x  = kron(ops{1}.HI,I{2});
            B_x = e_e*e_e' - e_w*e_w';
            M_x = Dm_x-H_x*B_x;
            D2_x = @(Viscosity) M_x*Viscosity*Dp_x;

            e_n = kron(I{1},ops{2}.e_r);
            e_s = kron(I{1},ops{2}.e_l);
            Dm_y = kron(I{1},ops{2}.Dm);
            Dp_y  = kron(I{1},ops{2}.Dp);
            H_y = kron(I{1},ops{2}.HI);
            B_y = e_n*e_n' - e_s*e_s';
            M_y = Dm_y-H_y*B_y;
            D2_y = @(Viscosity) M_y*Viscosity*Dp_y;
            D2 = @(Viscosity) D2_x(Viscosity) + D2_y(Viscosity);
        otherwise
            error('3D not yet implemented')
    end
end