diff --git a/pkgs/stdenv/linux/default.nix b/pkgs/stdenv/linux/default.nix
index dbaff342fb1..6a1211f9cc4 100644
--- a/pkgs/stdenv/linux/default.nix
+++ b/pkgs/stdenv/linux/default.nix
@@ -249,7 +249,7 @@ in
         # Apparently iconv won't work with bootstrap glibc, but it will be used
         # with glibc built later where we keep *this* build of libunistring,
         # so we need to trick it into supporting libiconv.
-        am_cv_func_iconv_works = "yes";
+        env = attrs.env or {} // { am_cv_func_iconv_works = "yes"; };
       });
       libidn2 = super.libidn2.overrideAttrs (attrs: {
         postFixup = attrs.postFixup or "" + ''