diff --git a/pkgs/by-name/at/atinout/package.nix b/pkgs/by-name/at/atinout/package.nix
index 64609395b210..e349edaf2658 100644
--- a/pkgs/by-name/at/atinout/package.nix
+++ b/pkgs/by-name/at/atinout/package.nix
@@ -10,8 +10,13 @@ stdenv.mkDerivation {
   pname = "atinout";
   version = "0.9.2-alpha";
 
-  env.NIX_CFLAGS_COMPILE = lib.optionalString (!stdenv.cc.isClang) "-Werror=implicit-fallthrough=0";
-  LANG = if stdenv.hostPlatform.isDarwin then "en_US.UTF-8" else "C.UTF-8";
+  env = {
+    LANG = if stdenv.hostPlatform.isDarwin then "en_US.UTF-8" else "C.UTF-8";
+  }
+  // lib.optionalAttrs (!stdenv.cc.isClang) {
+    NIX_CFLAGS_COMPILE = "-Werror=implicit-fallthrough=0";
+  };
+
   nativeBuildInputs = [
     ronn
     mount