diff --git a/nix/overlays/xonsh.nix b/nix/overlays/xonsh.nix
index 3ba5129..1d1b0c7 100644
--- a/nix/overlays/xonsh.nix
+++ b/nix/overlays/xonsh.nix
@@ -12,10 +12,10 @@ final: prev: {
 
   python39 = prev.python39.override {
     self = prev.python39;
-    packageOverrides = pself: psuper: {
-      prompt-toolkit = psuper.prompt-toolkit.overrideAttrs (old: rec {
+    packageOverrides = python_final: python_super: {
+      prompt-toolkit = python_super.prompt-toolkit.overrideAttrs (old: rec {
         version = "3.0.29";
-        src = final.python3Packages.fetchPypi {
+        src = python_final.fetchPypi {
           pname = "prompt_toolkit";
           inherit version;
           sha256 = "sha256-vWQPYOjOzXTw3CSXE9QzrOLdxitl7gf5bTWOCxUrbqc=";
@@ -24,7 +24,8 @@ final: prev: {
     };
   };
 
-  # Mach-nix is a toolkit for constructing custom Python environments
+  # Using mach-nix to fetch unpackaged xontrib plugins
+  # adapted from https://github.com/NixOS/nixpkgs/issues/75786#issuecomment-873654103
   mach-nix = import (builtins.fetchGit {
     url = "https://github.com/DavHau/mach-nix/";
     ref = "refs/tags/3.4.0";