diff --git a/pkgs/build-support/fetchgit/default.nix b/pkgs/build-support/fetchgit/default.nix
index 66bb3b7..83811e8 100644
--- a/pkgs/build-support/fetchgit/default.nix
+++ b/pkgs/build-support/fetchgit/default.nix
@@ -27,6 +27,7 @@ lib.makeOverridable (
 , # Impure env vars (https://nixos.org/nix/manual/#sec-advanced-attributes)
   # needed for netrcPhase
   netrcImpureEnvVars ? []
+, passthru ? {}
 , meta ? {}
 , allowedRequisites ? null
 }:
@@ -103,7 +104,7 @@ stdenvNoCC.mkDerivation {
 
   inherit preferLocalBuild meta allowedRequisites;
 
-  passthru = {
+  passthru = passthru // {
     gitRepoUrl = url;
   };
 }