def _update_page_resources(*, page, font, font_key, procset):
    """Update this page's fonts with a reference to the Glyphless font"""

    if '/Resources' not in page:
        page['/Resources'] = pikepdf.Dictionary({})
    resources = page['/Resources']
    try:
        fonts = resources['/Font']
    except KeyError:
        fonts = pikepdf.Dictionary({})
    if font_key is not None and font_key not in fonts:
        fonts[font_key] = font
    resources['/Font'] = fonts

    # Reassign /ProcSet to one that just lists everything - ProcSet is
    # obsolete and doesn't matter but recommended for old viewer support
    resources['/ProcSet'] = procset