Let X and Y be topological spaces and f : X → Y be a continuous function. We are interested in finding points of X and Y at which f is open. We will show that if X is developable, the set of points of openness of f in X is a G δ subset of X. If X is developable and f is closed, then the set of points of openness of f in Y is a G δ subset of Y. These will extend some results of S. Levi