RStudio doesn't start

I installed RStudio as per these instructions (on a system with NixOS 18.09).

However I get

qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

fish: “rstudio” terminated by signal SIGABRT (Abort)

A quick look at the qt packages didn’t reveal an xcb. Do you have any suggestions?