Contourf plot with uneven axes

I am trying to plot a contourf plot that has uneven axes, like so:

using Plots

contourf(Float64[k for k in 0:19], Float64[k for k in 0:2:38], rand(20,20))

This produces a plot like on the left:

Whereas I would like the contour plot to have rectangular dimensions scaled like the range of the axes like on the right.

Changing the aspect keyword to :equal, :none or a number doesn’t appear to have any effect. Is there a way to achieve this? Any plot backend is acceptable.

I figured out the problem. It seems aspect is not one of the valid aliases of the aspect_ratio subplot attribute: