diff --git a/pkgs/by-name/ef/eflite/package.nix b/pkgs/by-name/ef/eflite/package.nix
index a6aa478947e8..c797057b331f 100644
--- a/pkgs/by-name/ef/eflite/package.nix
+++ b/pkgs/by-name/ef/eflite/package.nix
@@ -44,7 +44,9 @@ stdenv.mkDerivation (finalAttrs: {
     ./format.patch
   ];
 
-  CFLAGS = lib.optionalString debug " -DDEBUG=2";
+  env = lib.optionalAttrs debug {
+    CFLAGS = " -DDEBUG=2";
+  };
 
   meta = {
     homepage = "https://eflite.sourceforge.net";