diff --git a/pkgs/by-name/he/helm/package.nix b/pkgs/by-name/he/helm/package.nix
index 96c3fa7b7457..1d71ea4ee24a 100644
--- a/pkgs/by-name/he/helm/package.nix
+++ b/pkgs/by-name/he/helm/package.nix
@@ -49,7 +49,7 @@ stdenv.mkDerivation (finalAttrs: {
   ];
   nativeBuildInputs = [ pkg-config ];
 
-  CXXFLAGS = [
+  env.CXXFLAGS = toString [
     "-DHAVE_LROUND"
     "-fpermissive"
   ];