Attribute 'field_classes' is ignored when using with Admin GenericInlineForms

When I'm trying to change image field class with field_classes and use it in GenericTabularInline - nothing happens and Django's default ImageField is used.

admin.py

class ImageAttachmentForm(ModelForm):

    class Meta:

        model = ImageAttachment

        fields = ['image']

        field_classes = {

            'image': CustomImageFormField,

        }

class ImageAttachmentInline(GenericTabularInline):

    form = ImageAttachmentForm

    model = ImageAttachment

@admin.register(Pet)

class PetAdmin(ModelAdmin):

    inlines = [ImageAttachmentInline]

I've submitted a probable fix here: https://github.com/Tuoris/django/commit/b7151a0860363487d120e168866c9b95e715b526

Thanks, tuoris