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 d6b719faa300..a0e0ebed2f6e 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
@@ -198,13 +198,15 @@ def get_main_parser() -> argparse.ArgumentParser:
 
 def parse_args(
     argv: list[str],
-) -> tuple[argparse.Namespace, dict[str, argparse.Namespace]]:
+) -> tuple[argparse.Namespace, GroupedNixArgs]:
     parser, sub_parsers = get_parser()
     args = parser.parse_args(argv[1:])
-    args_groups = {
-        group: parser.parse_known_args(argv[1:])[0]
-        for group, parser in sub_parsers.items()
-    }
+    grouped_nix_args = GroupedNixArgs.from_parsed_args_groups(
+        {
+            group: parser.parse_known_args(argv[1:])[0]
+            for group, parser in sub_parsers.items()
+        }
+    )
 
     if args.help or args.action is None:
         if WITH_SHELL_FILES:
@@ -266,12 +268,11 @@ def parse_args(
     if args.flake and (args.file or args.attr):
         parser.error("--flake cannot be used with --file or --attr")
 
-    return args, args_groups
+    return args, grouped_nix_args
 
 
 def execute(argv: list[str]) -> None:
-    args, args_groups = parse_args(argv)
-    grouped_nix_args = GroupedNixArgs.from_parsed_args_groups(args_groups)
+    args, grouped_nix_args = parse_args(argv)
 
     if args.upgrade or args.upgrade_all:
         nix.upgrade_channels(args.upgrade_all, args.sudo)
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 73187861c780..4c5f67196234 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
@@ -65,8 +65,7 @@ def test_parse_args() -> None:
     assert r1.install_grub is True
     assert r1.profile_name == "system"
     assert r1.action == "switch"
-    # round-trip test (ensure that we have the same flags as parsed)
-    assert nr.utils.dict_to_flags(vars(g1["common_flags"])) == [
+    assert nr.utils.dict_to_flags(g1.common_flags) == [
         "--option",
         "foo1",
         "bar1",
@@ -74,7 +73,13 @@ def test_parse_args() -> None:
         "foo2",
         "bar2",
     ]
-    assert nr.utils.dict_to_flags(vars(g1["flake_common_flags"])) == [
+    assert nr.utils.dict_to_flags(g1.flake_common_flags) == [
+        "--option",
+        "foo1",
+        "bar1",
+        "--option",
+        "foo2",
+        "bar2",
         "--update-input",
         "input1",
         "--update-input",
@@ -112,13 +117,15 @@ def test_parse_args() -> None:
     assert r2.action == "dry-build"
     assert r2.file == "foo"
     assert r2.attr == "bar"
-    # round-trip test (ensure that we have the same flags as parsed)
-    assert nr.utils.dict_to_flags(vars(g2["common_flags"])) == [
+    assert nr.utils.dict_to_flags(g2.common_flags) == [
         "-vvv",
         "--quiet",
         "--quiet",
     ]
-    assert nr.utils.dict_to_flags(vars(g2["common_build_flags"])) == [
+    assert nr.utils.dict_to_flags(g2.build_flags) == [
+        "-vvv",
+        "--quiet",
+        "--quiet",
         "--include",
         "include1",
         "--include",