diff --git a/README.md b/README.md
index 8fbe290..70e3ac3 100644
--- a/README.md
+++ b/README.md
@@ -23,8 +23,18 @@ to be customized, for example:
 let
 
   project = pkgs.callPackage ./yarn-project.nix {
+
+    # Example of providing a different source.
+    src = fetchFromGitHub {
+      owner = "johndoe";
+      repo = "myproject";
+      rev = "v1.0.0";
+      sha256 = "1hdhafj726g45gh7nj8qv1xls8mps3vhzq3aasdymbdqcb1clhkz";
+    };
+
     # Example of selecting a specific version of Node.js.
     nodejs = pkgs.nodejs-14_x;
+
   };
 
 in project.overrideAttrs (oldAttrs: {
diff --git a/src/yarn-project.nix.in b/src/yarn-project.nix.in
index cd8acdc..bc10ca7 100644
--- a/src/yarn-project.nix.in
+++ b/src/yarn-project.nix.in
@@ -1,7 +1,7 @@
 # This file is generated by running "yarn install" inside your project.
 # Manual changes might be lost - proceed with caution!
 
-{ lib, bash, coreutils, nodejs, perl, stdenv, writeText }:
+{ lib, coreutils, nodejs, stdenv, src ? ./. }:
 
 with lib;
 
@@ -23,9 +23,9 @@ let
 
   # Directory of just the files needed to run Yarn.
   yarn-closure = cleanSourceWith {
-    src = ./.;
+    inherit src;
     filter = let
-      srcStr = toString ./.;
+      srcStr = toString src;
       srcRel = removePrefix "${srcStr}/";
     in path: type:
       elem "${type}:${srcRel path}" yarn-closure-entries;
@@ -71,7 +71,7 @@ let
 
 in stdenv.mkDerivation {
   name = project-name;
-  src = ./.;
+  inherit src;
 
   # Tell node-gyp to use the provided Node.js headers for native code builds.
   npm_config_nodedir = nodejs;