diff --git a/pkgs/by-name/mi/mitra/package.nix b/pkgs/by-name/mi/mitra/package.nix
index 52c86feb8c44..7a62527e4d4f 100644
--- a/pkgs/by-name/mi/mitra/package.nix
+++ b/pkgs/by-name/mi/mitra/package.nix
@@ -21,7 +21,7 @@ rustPlatform.buildRustPackage rec {
   # require running database
   doCheck = false;
 
-  RUSTFLAGS = [
+  env.RUSTFLAGS = toString [
     # MEMO: mitra use ammonia crate with unstable rustc flag
     "--cfg=ammonia_unstable"
   ];