diff --git a/pkgs/stdenv/generic/default.nix b/pkgs/stdenv/generic/default.nix
index 372fd3cfa526..978da2e19070 100644
--- a/pkgs/stdenv/generic/default.nix
+++ b/pkgs/stdenv/generic/default.nix
@@ -128,8 +128,7 @@ let
       throwEvalHelp = { reason, errormsg }:
         # uppercase the first character of string s
         let up = s: with lib;
-          let cs = lib.stringToCharacters s;
-          in concatStrings (singleton (toUpper (head cs)) ++ tail cs);
+          (toUpper (substring 0 1 s)) + (substring 1 (stringLength s) s);
         in
         assert builtins.elem reason ["unfree" "broken" "blacklisted"];