cannot write mode P as WEBP

[chadsaun]

I have a .png image that is throwing this error:

cannot write mode P as WEBP

from the line with self.image.save in Willow:

    @Image.operation
    def save_as_webp(self, f, quality=80, lossless=False):
        self.image.save(f, 'WEBP', quality=quality, lossless=lossless) …
        return WebPImageFile(f)