diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/__init__.py b/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/__init__.py
index 99391ecf0c98..0ee3c6db0fd7 100644
--- a/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/__init__.py
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/__init__.py
@@ -217,7 +217,7 @@ def execute(argv: list[str]) -> None:
                 else:
                     if build_host:
                         path_to_config = nix.nixos_remote_build(
-                            "system",
+                            "toplevel",
                             build_attr,
                             build_host,
                             instantiate_flags=common_flags,
@@ -226,7 +226,7 @@ def execute(argv: list[str]) -> None:
                         )
                     else:
                         path_to_config = nix.nixos_build(
-                            "system",
+                            "toplevel",
                             build_attr,
                             no_out_link=True,
                             **build_flags,
@@ -275,7 +275,7 @@ def execute(argv: list[str]) -> None:
                 )
             else:
                 path_to_config = nix.nixos_build(
-                    "system",
+                    "toplevel",
                     build_attr,
                     dry_run=dry_run,
                     **build_flags,
diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/nix.py b/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/nix.py
index 317c04467a5d..a48dc18d9bf2 100644
--- a/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/nix.py
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/nix.py
@@ -261,7 +261,7 @@ def nixos_build(
         "nix-build",
         build_attr.path,
         "--attr",
-        f"{'.'.join(x for x in [build_attr.attr, attr] if x)}",
+        f"{build_attr.attr + '.' if build_attr.attr else ''}config.system.build.{attr}",
         *dict_to_flags(build_flags),
     ]
     r = run_wrapper(run_args, stdout=PIPE)
@@ -303,7 +303,7 @@ def nixos_remote_build(
             "--raw",
             build_attr.path,
             "--attr",
-            f"{'.'.join(x for x in [build_attr.attr, attr] if x)}",
+            f"{build_attr.attr + '.' if build_attr.attr else ''}config.system.build.{attr}",
             *dict_to_flags(instantiate_flags or {}),
         ],
         stdout=PIPE,
diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_main.py b/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_main.py
index eeecf9445978..b5c93a2dd217 100644
--- a/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_main.py
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_main.py
@@ -122,7 +122,7 @@ def test_execute_nix_boot(mock_run: Any, tmp_path: Path) -> None:
                     "nix-build",
                     "<nixpkgs/nixos>",
                     "--attr",
-                    "system",
+                    "config.system.build.toplevel",
                     "--no-out-link",
                     "-vvv",
                 ],
diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_nix.py b/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_nix.py
index 712bd09b8704..dce98cf6b939 100644
--- a/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_nix.py
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_nix.py
@@ -251,7 +251,14 @@ def test_nixos_build(mock_run: Any, monkeypatch: Any) -> None:
         "attr", m.BuildAttr("<nixpkgs/nixos>", None), nix_flag="foo"
     ) == Path("/path/to/file")
     mock_run.assert_called_with(
-        ["nix-build", "<nixpkgs/nixos>", "--attr", "attr", "--nix-flag", "foo"],
+        [
+            "nix-build",
+            "<nixpkgs/nixos>",
+            "--attr",
+            "config.system.build.attr",
+            "--nix-flag",
+            "foo",
+        ],
         stdout=PIPE,
     )
 
@@ -259,7 +266,7 @@ def test_nixos_build(mock_run: Any, monkeypatch: Any) -> None:
         "/path/to/file"
     )
     mock_run.assert_called_with(
-        ["nix-build", Path("file"), "--attr", "preAttr.attr"],
+        ["nix-build", Path("file"), "--attr", "preAttr.config.system.build.attr"],
         stdout=PIPE,
     )
 
@@ -332,7 +339,7 @@ def test_nixos_remote_build(mock_run: Any, monkeypatch: Any) -> None:
     build_host = m.Remote("user@host", ["--ssh", "opts"], None)
     assert n.nixos_remote_build(
         "attr",
-        m.BuildAttr("<nixpkgs/nixos>", None),
+        m.BuildAttr("<nixpkgs/nixos>", "preAttr"),
         build_host,
         build_flags={"build": True},
         instantiate_flags={"inst": True},
@@ -346,7 +353,7 @@ def test_nixos_remote_build(mock_run: Any, monkeypatch: Any) -> None:
                     "--raw",
                     "<nixpkgs/nixos>",
                     "--attr",
-                    "attr",
+                    "preAttr.config.system.build.attr",
                     "--inst",
                 ],
                 stdout=PIPE,