diff --git a/nix-support/build/outputs.nix b/nix-support/build/outputs.nix
index 9c393e2a0..7b1c45852 100644
--- a/nix-support/build/outputs.nix
+++ b/nix-support/build/outputs.nix
@@ -139,16 +139,6 @@ lib.fix (self: {
     # Binary package for various platforms.
     build = forAllSystems (system: self.packages.${system}.nix);
 
-    # Ensure support for lowdown < 3.0 doesn't regress for NixOS 25.11
-    build-lowdown_2_0 = lib.genAttrs [ "aarch64-linux" ] (
-      system:
-      assert lib.versionOlder nixpkgsFor.${system}.native.lowdown.version "3.0.0";
-      self.packages.${system}.nix.override {
-        lowdown = nixpkgsFor.${system}.native.lowdown;
-        lowdown-unsandboxed = nixpkgsFor.${system}.native.lowdown-unsandboxed;
-      }
-    );
-
     buildStatic = lib.genAttrs linux64BitSystems (system: self.packages.${system}.nix-static);
 
     rl-next = forAllSystems (
@@ -208,5 +198,15 @@ lib.fix (self: {
         doCheck = false;
         doInstallCheck = false;
       });
+  }
+  // lib.optionalAttrs (nixpkgsFor ? aarch64-linux) {
+    build-lowdown_2_0 = lib.genAttrs [ "aarch64-linux" ] (
+      system:
+      assert lib.versionOlder nixpkgsFor.${system}.native.lowdown.version "3.0.0";
+      self.packages.${system}.nix.override {
+        lowdown = nixpkgsFor.${system}.native.lowdown;
+        lowdown-unsandboxed = nixpkgsFor.${system}.native.lowdown-unsandboxed;
+      }
+    );
   };
 })
diff --git a/tests/nixos/default.nix b/tests/nixos/default.nix
index fff155497..dce4566d9 100644
--- a/tests/nixos/default.nix
+++ b/tests/nixos/default.nix
@@ -8,6 +8,8 @@ let
 
   nixos-lib = import (nixpkgs + "/nixos/lib") { };
 
+  filterPlatforms = lib.filter (p: nixpkgsFor?${p});
+
   # https://nixos.org/manual/nixos/unstable/index.html#sec-calling-nixos-tests
   runNixOSTestFor =
     system: test:
@@ -186,7 +188,7 @@ in
 
   cgroups = runNixOSTestFor "x86_64-linux" ./cgroups;
 
-  setuid = lib.genAttrs [ "i686-linux" "x86_64-linux" ] (
+  setuid = lib.genAttrs (filterPlatforms [ "i686-linux" "x86_64-linux" ]) (
     system: runNixOSTestFor system ./setuid/setuid.nix
   );