diff --git a/pkgs/by-name/pr/proxmox-backup-client/package.nix b/pkgs/by-name/pr/proxmox-backup-client/package.nix
index 46461df67457..1ba669faae8b 100644
--- a/pkgs/by-name/pr/proxmox-backup-client/package.nix
+++ b/pkgs/by-name/pr/proxmox-backup-client/package.nix
@@ -124,13 +124,14 @@ rustPlatform.buildRustPackage {
     "--bin=pxar"
   ];
 
-  RUSTFLAGS = [ "-L.dep-stubs" ];
+  env = {
+    RUSTFLAGS = toString [ "-L.dep-stubs" ];
+    # pbs-buildcfg requires this set, would be the git commit id
+    REPOID = "";
+  };
 
   doCheck = false;
 
-  # pbs-buildcfg requires this set, would be the git commit id
-  REPOID = "";
-
   nativeBuildInputs = [
     pkgconf
     rustPlatform.bindgenHook