diff --git a/nixos/hosts/nixos-rpi4-img/default.nix b/nixos/hosts/nixos-rpi4-img/default.nix
index 5b2e6779..11ae1642 100644
--- a/nixos/hosts/nixos-rpi4-img/default.nix
+++ b/nixos/hosts/nixos-rpi4-img/default.nix
@@ -2,7 +2,7 @@
   # Build this image with:
   # nix build .#nixosConfigurations.nixos-rpi4-img.config.system.build.sdImage
   nixpkgs.hostPlatform = lib.mkDefault "aarch64-linux";
-  nixpkgs.buildPlatform.system = $platform;
+  nixpkgs.buildPlatform.system = "${platform}";
   networking.hostName = "nixos-rpi4-img";
   networking.firewall.allowedTCPPorts = [ 22 ];
 }
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