def validate_geometry(screen_geometry):
    """Raise ValueError if 'screen_geometry' does not conform to <integer>x<integer> format"""
    columns, rows = [int(value) for value in screen_geometry.lower().split('x')]
    if columns <= 0 or rows <= 0:
        raise ValueError('Invalid value for screen-geometry option: "{}"'.format(screen_geometry))
    return columns, rows