--- a/lib/flakePart.nix
+++ b/lib/flakePart.nix
@@ -33,6 +33,8 @@
           # To use user-provided nixpkgs, we first need to extract wanted nixpkgs attribute,
           # to do that, evaluate all the modules with only needed option declared.
           bootstrapEval = lib.evalModules {
+            class = "fleet";
+            prefix = ["fleetConfiguration"];
             modules = [
               module
               {
@@ -50,6 +52,8 @@
           };
           bootstrapNixpkgs = bootstrapEval.config.nixpkgs.buildUsing;
           normalEval = bootstrapNixpkgs.lib.evalModules {
+            class = "fleet";
+            prefix = ["fleetConfiguration"];
             modules = (import ../modules/module-list.nix) ++ [
               module
               (
--- a/modules/nixos.nix
+++ b/modules/nixos.nix
@@ -37,14 +37,17 @@
             module:
             let
               inherit (hostArgs.config) system;
+              modulesPath = "${config.nixpkgs.buildUsing}/nixos/modules";
             in
             config.nixpkgs.buildUsing.lib.evalModules {
-              modules = (import "${config.nixpkgs.buildUsing}/nixos/modules/module-list.nix") ++ [
+              class = "nixos";
+              prefix = ["fleetConfiguration" "hosts" hostArgs.config._module.args.name "nixos"];
+              modules = (import "${modulesPath}/module-list.nix") ++ [
                 (module // { key = "attr<host.nixos>"; })
                 (config.nixos // { key = "attr<fleet.nixos>"; })
               ];
               specialArgs = {
-                inherit fleetLib inputs self;
+                inherit fleetLib inputs self modulesPath;
                 inputs' = mapAttrs (
                   inputName: input:
                   builtins.addErrorContext
@@ -56,6 +59,9 @@
                         "input is not a flake, perhaps flake = false was added to te input declaration?"
                     )
                 ) inputs;
+                self' = builtins.addErrorContext "while retrieving system-dependent attributes for a flake's own outputs" (
+                  _fleetFlakeRootConfig.perInput system self
+                );
               };
             };
         };
@@ -68,7 +74,7 @@
         #   (mkRemovedOptionModule ["nixosModules"] "replaced with hosts.*.nixos.imports.")
         # ];
         nixos = {
-          config._module.args = {
+          _module.args = {
             nixosHosts = mapAttrs (_: value: value.nixos_unchecked.config) config.hosts;
             hosts = config.hosts;
             host = hostArgs.config;