From 79aec2d4bf0bee9bae16df5cbb0be4bc2917ae16 Mon Sep 17 00:00:00 2001
From: Eman Resu <78693624+quatquatt@users.noreply.github.com>
Date: Mon, 27 Apr 2026 11:02:21 -0400
Subject: [PATCH] stdenv.mkDerivation: avoid // merge if meta.mainProgram not
 set

---
 pkgs/stdenv/generic/make-derivation.nix | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/pkgs/stdenv/generic/make-derivation.nix b/pkgs/stdenv/generic/make-derivation.nix
index 12a6dffb426f..f7c935168852 100644
--- a/pkgs/stdenv/generic/make-derivation.nix
+++ b/pkgs/stdenv/generic/make-derivation.nix
@@ -806,9 +806,7 @@ let
       );
 
     let
-      env' = env // {
-        ${if meta ? mainProgram then "NIX_MAIN_PROGRAM" else null} = meta.mainProgram;
-      };
+      env' = if meta ? mainProgram then env // { NIX_MAIN_PROGRAM = meta.mainProgram; } else env;
 
       derivationArg = makeDerivationArgument (
         removeAttrs attrs [