diff --git a/nixos/modules/misc/nixpkgs.nix b/nixos/modules/misc/nixpkgs.nix
index caf57d7d6371..e1c705eef3b5 100644
--- a/nixos/modules/misc/nixpkgs.nix
+++ b/nixos/modules/misc/nixpkgs.nix
@@ -73,10 +73,7 @@ let
   defaultPkgs =
     if opt.hostPlatform.isDefined then
       let
-        isCross =
-          !(lib.systems.equals (lib.systems.elaborate cfg.buildPlatform) (
-            lib.systems.elaborate cfg.hostPlatform
-          ));
+        isCross = cfg.buildPlatform != cfg.hostPlatform;
         systemArgs =
           if isCross then
             {
@@ -198,10 +195,13 @@ in
     };
 
     hostPlatform = lib.mkOption {
-      type = lib.types.either lib.types.str lib.types.attrs;
+      type = lib.types.either lib.types.str lib.types.attrs; # TODO utilize lib.systems.parsedPlatform
       example = {
         system = "aarch64-linux";
       };
+      # Make sure that the final value has all fields for sake of other modules
+      # referring to this. TODO make `lib.systems` itself use the module system.
+      apply = lib.systems.elaborate;
       defaultText = lib.literalExpression ''(import "''${nixos}/../lib").lib.systems.examples.aarch64-multiplatform'';
       description = ''
         Specifies the platform where the NixOS configuration will run.
@@ -213,13 +213,22 @@ in
     };
 
     buildPlatform = lib.mkOption {
-      type = lib.types.either lib.types.str lib.types.attrs;
+      type = lib.types.either lib.types.str lib.types.attrs; # TODO utilize lib.systems.parsedPlatform
       default = cfg.hostPlatform;
       example = {
         system = "x86_64-linux";
       };
       # Make sure that the final value has all fields for sake of other modules
       # referring to this.
+      apply =
+        inputBuildPlatform:
+        let
+          elaborated = lib.systems.elaborate inputBuildPlatform;
+        in
+        if lib.systems.equals elaborated cfg.hostPlatform then
+          cfg.hostPlatform # make identical, so that `==` equality works; see https://github.com/NixOS/nixpkgs/issues/278001
+        else
+          elaborated;
       defaultText = lib.literalExpression ''config.nixpkgs.hostPlatform'';
       description = ''
         Specifies the platform on which NixOS should be built.
@@ -236,11 +245,14 @@ in
     };
 
     localSystem = lib.mkOption {
-      type = lib.types.attrs;
+      type = lib.types.attrs; # TODO utilize lib.systems.parsedPlatform
       default = { inherit (cfg) system; };
       example = {
         system = "aarch64-linux";
       };
+      # Make sure that the final value has all fields for sake of other modules
+      # referring to this. TODO make `lib.systems` itself use the module system.
+      apply = lib.systems.elaborate;
       defaultText = lib.literalExpression ''(import "''${nixos}/../lib").lib.systems.examples.aarch64-multiplatform'';
       description = ''
         Systems with a recently generated `hardware-configuration.nix`
@@ -268,7 +280,7 @@ in
     #      is a relation between at least 2 systems in the context of a
     #      specific build step, not a single system.
     crossSystem = lib.mkOption {
-      type = lib.types.nullOr lib.types.attrs;
+      type = lib.types.nullOr lib.types.attrs; # TODO utilize lib.systems.parsedPlatform
       default = null;
       example = {
         system = "aarch64-linux";
@@ -404,18 +416,6 @@ in
             ${lib.concatMapStringsSep "\n" (file: "  - ${file}") opt.config.files}
           '';
         }
-        {
-          assertion =
-            (opt.hostPlatform.isDefined -> builtins.isAttrs cfg.buildPlatform -> !(cfg.buildPlatform ? parsed))
-            && (opt.hostPlatform.isDefined -> builtins.isAttrs cfg.hostPlatform -> !(cfg.hostPlatform ? parsed))
-            && (builtins.isAttrs cfg.localSystem -> !(cfg.localSystem ? parsed))
-            && (builtins.isAttrs cfg.crossSystem -> !(cfg.crossSystem ? parsed));
-          message = ''
-            Passing fully elaborated systems to `nixpkgs.localSystem`, `nixpkgs.crossSystem`, `nixpkgs.buildPlatform`
-            or `nixpkgs.hostPlatform` will break composability of package sets in nixpkgs. For example, pkgs.pkgsStatic
-            would not work in modules anymore.
-          '';
-        }
       ];
   };
 
diff --git a/nixos/modules/misc/nixpkgs/read-only.nix b/nixos/modules/misc/nixpkgs/read-only.nix
index 9d0d452ba52d..fa372d13e545 100644
--- a/nixos/modules/misc/nixpkgs/read-only.nix
+++ b/nixos/modules/misc/nixpkgs/read-only.nix
@@ -40,11 +40,20 @@ in
           The Nixpkgs overlays that `pkgs` was initialized with.
         '';
       };
-      # buildPlatform and hostPlatform left out on purpose:
-      # - They are not supposed to be changed with this read-only module.
-      # - They are not supposed to be read either, according to the description
-      #   of "system" in the traditional nixpkgs module.
-      #
+      hostPlatform = mkOption {
+        internal = true;
+        readOnly = true;
+        description = ''
+          The platform of the machine that is running the NixOS configuration.
+        '';
+      };
+      buildPlatform = mkOption {
+        internal = true;
+        readOnly = true;
+        description = ''
+          The platform of the machine that built the NixOS configuration.
+        '';
+      };
       # NOTE: do not add the legacy options such as localSystem here. Let's keep
       #       this module simple and let module authors upgrade their code instead.
     };
@@ -52,8 +61,12 @@ in
   config = {
     _module.args.pkgs =
       # find mistaken definitions
-      builtins.seq cfg.config builtins.seq cfg.overlays cfg.pkgs;
+      builtins.seq cfg.config builtins.seq cfg.overlays builtins.seq cfg.hostPlatform builtins.seq
+        cfg.buildPlatform
+        cfg.pkgs;
     nixpkgs.config = cfg.pkgs.config;
     nixpkgs.overlays = cfg.pkgs.overlays;
+    nixpkgs.hostPlatform = cfg.pkgs.stdenv.hostPlatform;
+    nixpkgs.buildPlatform = cfg.pkgs.stdenv.buildPlatform;
   };
 }
diff --git a/nixos/modules/virtualisation/nixos-containers.nix b/nixos/modules/virtualisation/nixos-containers.nix
index 036f5129b1b3..5f43e3322340 100644
--- a/nixos/modules/virtualisation/nixos-containers.nix
+++ b/nixos/modules/virtualisation/nixos-containers.nix
@@ -506,12 +506,8 @@ in
                         config = {
                           nixpkgs =
                             if options.nixpkgs?hostPlatform
-                            then {
-                              hostPlatform =
-                                if host.options.nixpkgs.hostPlatform.isDefined
-                                then host.config.nixpkgs.hostPlatform
-                                else lib.defaultTo host.config.nixpkgs.localSystem host.config.nixpkgs.crossSystem;
-                            } else { localSystem = lib.defaultTo host.config.nixpkgs.localSystem host.config.nixpkgs.crossSystem; }
+                            then { inherit (host.pkgs.stdenv) hostPlatform; }
+                            else { localSystem = host.pkgs.stdenv.hostPlatform; }
                           ;
                           boot.isContainer = true;
                           networking.hostName = mkDefault name;
diff --git a/nixos/tests/appliance-repart-image-verity-store.nix b/nixos/tests/appliance-repart-image-verity-store.nix
index 4769dd052e87..ef0fda4f780d 100644
--- a/nixos/tests/appliance-repart-image-verity-store.nix
+++ b/nixos/tests/appliance-repart-image-verity-store.nix
@@ -40,7 +40,7 @@
         verityStore = {
           enable = true;
           # by default the module works with systemd-boot, for simplicity this test directly boots the UKI
-          ukiPath = "/EFI/BOOT/BOOT${lib.toUpper pkgs.stdenv.hostPlatform.efiArch}.EFI";
+          ukiPath = "/EFI/BOOT/BOOT${lib.toUpper config.nixpkgs.hostPlatform.efiArch}.EFI";
         };
 
         name = "appliance-verity-store-image";
@@ -51,7 +51,7 @@
             repartConfig = {
               Type = "esp";
               Format = "vfat";
-              SizeMinBytes = if pkgs.stdenv.hostPlatform.isx86_64 then "64M" else "96M";
+              SizeMinBytes = if config.nixpkgs.hostPlatform.isx86_64 then "64M" else "96M";
             };
           };
           ${partitionIds.store-verity}.repartConfig = {
diff --git a/nixos/tests/appliance-repart-image.nix b/nixos/tests/appliance-repart-image.nix
index b916875bfcea..11447cf8fa03 100644
--- a/nixos/tests/appliance-repart-image.nix
+++ b/nixos/tests/appliance-repart-image.nix
@@ -53,7 +53,7 @@ in
           "esp" = {
             contents =
               let
-                efiArch = pkgs.stdenv.hostPlatform.efiArch;
+                efiArch = config.nixpkgs.hostPlatform.efiArch;
               in
               {
                 "/EFI/BOOT/BOOT${lib.toUpper efiArch}.EFI".source =
@@ -70,7 +70,7 @@ in
               # aarch64 kernel seems to generally be a little bigger than the
               # x86_64 kernel. To stay on the safe side, leave some more slack
               # for every platform other than x86_64.
-              SizeMinBytes = if pkgs.stdenv.hostPlatform.isx86_64 then "64M" else "96M";
+              SizeMinBytes = if config.nixpkgs.hostPlatform.isx86_64 then "64M" else "96M";
             };
           };
           "swap" = {
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 9b1537d6bdd0..2984ac2075d4 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -17721,7 +17721,7 @@ with pkgs;
                 [(
                   { lib, ... }: {
                     config.nixpkgs.pkgs = lib.mkDefault pkgs;
-                    config.nixpkgs.localSystem = lib.mkDefault ({ config = lib.systems.parse.tripleFromSystem stdenv.hostPlatform; });
+                    config.nixpkgs.localSystem = lib.mkDefault stdenv.hostPlatform;
                   }
                 )] ++ (
                   if builtins.isList configuration