diff --git a/pkgs/by-name/bi/bird2/package.nix b/pkgs/by-name/bi/bird2/package.nix
index a86924f8d47e..61e5c7b30057 100644
--- a/pkgs/by-name/bi/bird2/package.nix
+++ b/pkgs/by-name/bi/bird2/package.nix
@@ -37,7 +37,7 @@ stdenv.mkDerivation (finalAttrs: {
     ./dont-create-sysconfdir-2.patch
   ];
 
-  CPP = "${stdenv.cc.targetPrefix}cpp -E";
+  env.CPP = "${stdenv.cc.targetPrefix}cpp -E";
 
   configureFlags = [
     "--localstatedir=/var"