Genetic algorithm - Constraint Function

Objective function: f(x) = x(1) + 2*x(2) + 3*x(3) + 4*x(4)

Constraint function: x(1) + x(2) + x(3) + x(4) - 5 = 0

Based on the statement above, the constraint function of the GA must equal to 0 for the minimization. However, the GA in matlab only permit lesser or equal instead of absolute equal. As result, the minimization of my objective function does not achieve the number that I desired. Hence, any solutions for this problem?