diff --git a/source/reference/pinning-nixpkgs.rst b/source/reference/pinning-nixpkgs.rst
index def1c94..fb06871 100644
--- a/source/reference/pinning-nixpkgs.rst
+++ b/source/reference/pinning-nixpkgs.rst
@@ -35,8 +35,8 @@ Examples
 - ``NIX_PATH=nixpkgs=http://nixos.org/channels/nixos-20.03/nixexprs.tar.xz nix-build ...``
 - Using just Nix::
 
-    with import (fetchTarball https://github.com/NixOS/nixpkgs/archive/nixos-20.03.tar.gz) {};
-
-    stdenv.mkDerivation { … }
+    let
+      pkgs = import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/nixos-20.03.tar.gz") {};
+    in pkgs.stdenv.mkDerivation { … }
 
 - To make ad-hoc environment available on NixOS: ``nix.nixPath = [ ("nixpkgs=" + toString pkgs.path) ];``
diff --git a/source/tutorials/towards-reproducibility-pinning-nixpkgs.rst b/source/tutorials/towards-reproducibility-pinning-nixpkgs.rst
index 49641b7..cb84ad9 100644
--- a/source/tutorials/towards-reproducibility-pinning-nixpkgs.rst
+++ b/source/tutorials/towards-reproducibility-pinning-nixpkgs.rst
@@ -32,7 +32,7 @@ The simplest way to do this is to fetch the required nixpkgs version as a tarbal
 
 .. code:: nix
 
-    { pkgs ? import (fetchTarball https://github.com/NixOS/nixpkgs/archive/3590f02e7d5760e52072c1a729ee2250b5560746.tar.gz) {};
+    { pkgs ? import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/3590f02e7d5760e52072c1a729ee2250b5560746.tar.gz") {};
     }:
 
     ...