Adding scale bar to map made with ggRGB

I have made a RGB composite image of a satellite image using ggRGB() from the RStoolbox package. I would like to add a scale bar to the image, but I'm stumped as to how to do this. I would usually use scalebar() from the ggsn package when working with ggmaps() in R, but it doesn't look like it can handle a RasterBrick object as input like like is required for ggRGB().

Here is an example:

library(raster)
library(ggplot2)
library(RStoolbox)

data(lsat)

ggRGB(img = lsat,
      r = 3,
      g = 2,
      b = 1,
      stretch = 'hist') +
  blank() # eliminate x and y axes

This produces the following image:

I would like to add a scale bar in the upper right corner. Here's what I tried:

ggRGB(img = lsat,
      r = 3,
      g = 2,
      b = 1,
      stretch = 'hist') +
  blank() +
  ggsn::scalebar(lsat, dist = 2, dist_unit = "km",
                 transform = TRUE, model = "WGS84", location = "upperright")

This returns an error: "Error in .local(x, ...) : invalid layer names"

Any help would be much appreciated. I'd like to stick with ggRGB() if possible, but I'd be open to other plotting methods if I can place a scale bar on the image.

You could use package ggspatial

ggRGB(img = lsat,
      r = 3,
      g = 2,
      b = 1,
      stretch = 'hist') +
  theme_void() +
  ggspatial::annotation_scale(location = "tr", width_hint =0.5, pad_x = unit(0.7, "cm"))

If you want more fine control over the appearance, a slightly more verbose but highly customizable method is also given in this answer https://stackoverflow.com/a/39069955/2761575