diff --git a/pkgs/build-support/fetchgit/tests.nix b/pkgs/build-support/fetchgit/tests.nix
index a2f620b4b638..25bb55ed53bf 100644
--- a/pkgs/build-support/fetchgit/tests.nix
+++ b/pkgs/build-support/fetchgit/tests.nix
@@ -1,6 +1,5 @@
 {
-  stdenv,
-  config,
+  lib,
   runCommand,
   testers,
   fetchgit,
@@ -238,21 +237,15 @@
         hash = "sha256-7DszvbCNTjpzGRmpIVAWXk20P0/XTrWZ79KSOGLrUWY=";
       };
 
-  withGitConfig =
-    let
-      pkgs = import ../../.. {
-        system = stdenv.hostPlatform.system;
-        config = config // {
-          gitConfig = {
-            url."https://github.com".insteadOf = "https://doesntexist.forsure";
-          };
-        };
-      };
-    in
-    pkgs.testers.invalidateFetcherByDrvHash pkgs.fetchgit {
-      name = "fetchgit-with-config";
-      url = "https://doesntexist.forsure/NixOS/nix";
-      rev = "9d9dbe6ed05854e03811c361a3380e09183f4f4a";
-      sha256 = "sha256-7DszvbCNTjpzGRmpIVAWXk20P0/XTrWZ79KSOGLrUWY=";
-    };
+  withGitConfig = testers.invalidateFetcherByDrvHash fetchgit {
+    name = "fetchgit-with-config";
+    url = "https://doesntexist.forsure/NixOS/nix";
+    rev = "9d9dbe6ed05854e03811c361a3380e09183f4f4a";
+    sha256 = "sha256-7DszvbCNTjpzGRmpIVAWXk20P0/XTrWZ79KSOGLrUWY=";
+    gitConfigFile = lib.toFile "gitconfig" (
+      lib.generators.toGitINI {
+        url."https://github.com".insteadOf = "https://doesntexist.forsure";
+      }
+    );
+  };
 }