diff --git a/pkgs/tools/package-management/nix/common.nix b/pkgs/tools/package-management/nix/common.nix
index 946407826f25..670e2282aa20 100644
--- a/pkgs/tools/package-management/nix/common.nix
+++ b/pkgs/tools/package-management/nix/common.nix
@@ -216,7 +216,7 @@ self = stdenv.mkDerivation {
   # Prevent crashes in libcurl due to invoking Objective-C `+initialize` methods after `fork`.
   # See http://sealiesoftware.com/blog/archive/2017/6/5/Objective-C_and_fork_in_macOS_1013.html.
   + lib.optionalString stdenv.isDarwin ''
-    export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=yes
+    export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES
   ''
   # See https://github.com/NixOS/nix/issues/5687
   + lib.optionalString (atLeast25 && stdenv.isDarwin) ''