diff --git a/README.md b/README.md
index f4f49415..efdcb98b 100644
--- a/README.md
+++ b/README.md
@@ -146,9 +146,10 @@ You can find the full example in [`templates/devshell/`](./templates/devshell/).
 
 ### Pre-flakes usage
 
-The `default.nix` file in the root of this repo exposes all flake outputs as
-Nix attributes. This is useful for users who haven't yet made the jump to the
-Nix Flakes world.
+The `default.nix` file in the root of this repo is a
+[shim](https://nixos.wiki/wiki/Flakes#Using_flakes_with_stable_Nix) that
+exposes all flake outputs as Nix attributes. This is useful for users who
+haven't yet made the jump to the Nix Flakes world.
 
 For example, if you have an existing `shell.nix` file, all you need to do is add
 the changes marked as "NEW" from the snippet below:
@@ -178,6 +179,13 @@ in
 You can find the full example in
 [`templates/pre-flake-devshell/`](./templates/pre-flake-devshell/).
 
+It should be noted that unlike most traditional Nix projects, this will not
+build the compilers using your `<nixpkgs>`. Instead it will build them using a
+fixed Nixpkgs version defined in `flake.lock` of this project. Indeed this is
+one of the differences how things are usually done with and without flakes,
+even when it's possible to either pin or to not pin the nixpkgs version
+regardless of flake use.
+
 ## Source and binary variants
 
 DMD and LDC packages come in two variants: `binary` and `source`.