tkinterhtml.HtmlFrame.set_content() crashes when using 64-bit Python

I have both 32- and 64-bit Python installed on my Windows machine. When I run the below program with 32-bit, it works fine, but with 64-bit, when you click the button to open the HTML page, it crashes with Process finished with exit code -1073741819 (0xC0000005). Commenting out the line marked # this line makes it work, although obviously it doesn't display the HTML. How would I fix this?

import tkinter
from tkinter import ttk

import tkinterhtml


class Gui:
    root = None

    def open_html_page(self):
        local_root = tkinter.Toplevel(self.root)
        local_root.transient(self.root)
        local_root.grab_set()

        big_frame = ttk.Frame(local_root)
        big_frame.pack(fill='both', expand=True)

        html = "<b>This is an <i>HTML</i> page</b>"

        html_frame = tkinterhtml.HtmlFrame(local_root)
        html_frame.pack()
        print(html)
        html_frame.set_content(html) # this line

        local_root.mainloop()

    def launch_gui(self):
        self.root = tkinter.Tk()
        big_frame = ttk.Frame(self.root)
        big_frame.pack(fill='both', expand=True)

        open_html_button = ttk.Button(big_frame, text="Open HTML page", command=self.open_html_page)
        open_html_button.pack()

        self.root.mainloop()


def main():
    Gui().launch_gui()


if __name__ == '__main__':
    main()