diff --git a/mypy-baseline.txt b/mypy-baseline.txt
index 91ee96f00..6aed090c2 100644
--- a/mypy-baseline.txt
+++ b/mypy-baseline.txt
@@ -343,21 +343,8 @@ scripts/generate_installer_doc.py:0: error: Name "_install._OsRule" is not defin
 scripts/generate_launcher_index.py:0: error: Argument 1 to "module_from_spec" has incompatible type "Optional[ModuleSpec]"; expected "ModuleSpec"  [arg-type]
 scripts/generate_launcher_index.py:0: error: Item "None" of "Optional[ModuleSpec]" has no attribute "loader"  [union-attr]
 scripts/generate_launcher_index.py:0: error: Item "None" of "Union[Loader, Any, None]" has no attribute "exec_module"  [union-attr]
-scripts/generate_pack.py:0: error: Argument 1 to "_add_pack_member" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_add_pack_member" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_add_pack_member" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_add_pack_member" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_add_pack_member" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_add_pack_member" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
 scripts/generate_pack.py:0: error: Argument 1 to "_narrowings" has incompatible type "Union[str, bool]"; expected "str"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_pack_data_directories" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_pack_data_directories" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_pack_data_tree" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
 scripts/generate_pack.py:0: error: Argument 1 to "_release_asset_name" has incompatible type "Optional[str]"; expected "str"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_write_generated_member" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_write_generated_member" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_write_generated_member" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 1 to "_write_generated_member" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
 scripts/generate_pack.py:0: error: Argument 10 to "generate_pack" has incompatible type "**dict[str, Union[dict[Any, Any], Any, set[str], list[str], str, bool, None]]"; expected "Optional[bool]"  [arg-type]
 scripts/generate_pack.py:0: error: Argument 10 to "generate_pack" has incompatible type "**dict[str, Union[dict[Any, Any], Any, set[str], list[str], str, bool, None]]"; expected "Optional[dict[Any, Any]]"  [arg-type]
 scripts/generate_pack.py:0: error: Argument 10 to "generate_pack" has incompatible type "**dict[str, Union[dict[Any, Any], Any, set[str], list[str], str, bool, None]]"; expected "Optional[list[dict[Any, Any]]]"  [arg-type]
@@ -366,12 +353,6 @@ scripts/generate_pack.py:0: error: Argument 10 to "generate_pack" has incompatib
 scripts/generate_pack.py:0: error: Argument 10 to "generate_pack" has incompatible type "**dict[str, Union[dict[Any, Any], Any, set[str], list[str], str, bool, None]]"; expected "Optional[str]"  [arg-type]
 scripts/generate_pack.py:0: error: Argument 10 to "generate_pack" has incompatible type "**dict[str, Union[dict[Any, Any], Any, set[str], list[str], str, bool, None]]"; expected "bool"  [arg-type]
 scripts/generate_pack.py:0: error: Argument 10 to "generate_pack" has incompatible type "**dict[str, Union[dict[Any, Any], Any, set[str], list[str], str, bool, None]]"; expected "str"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 3 to "_add_zip_to_pack" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 3 to "_add_zip_to_pack" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 3 to "_add_zip_to_pack" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 3 to "_add_zip_to_pack" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 3 to "_extract_zip_to_archive" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
-scripts/generate_pack.py:0: error: Argument 3 to "_extract_zip_to_archive" has incompatible type "Union[PackRecord, ZipFile]"; expected "ZipFile"  [arg-type]
 scripts/generate_pack.py:0: error: Argument 4 to "_manifest_core_index" has incompatible type "dict_values[str, dict[Any, Any]]"; expected "list[dict[Any, Any]]"  [arg-type]
 scripts/generate_pack.py:0: error: Argument 4 to "_narrowings" has incompatible type "Union[str, bool]"; expected "bool"  [arg-type]
 scripts/generate_pack.py:0: error: Argument 5 to "_narrowings" has incompatible type "Union[str, bool]"; expected "bool"  [arg-type]
diff --git a/scripts/generate_pack.py b/scripts/generate_pack.py
index 03ef16791..d94a2975d 100644
--- a/scripts/generate_pack.py
+++ b/scripts/generate_pack.py
@@ -164,7 +164,9 @@ class PackRecord:
         self.sources: dict[str, str] = {}
 
 
-def _add_pack_member(zf: zipfile.ZipFile, source_path: str, arcname: str) -> None:
+def _add_pack_member(
+    zf: zipfile.ZipFile | PackRecord, source_path: str, arcname: str
+) -> None:
     """Add a file to the pack with metadata that does not depend on the build.
 
     ZipFile.write copies the source file's mtime into the member. For a file
@@ -197,7 +199,9 @@ def _add_pack_member(zf: zipfile.ZipFile, source_path: str, arcname: str) -> Non
         shutil.copyfileobj(source, target, 1024 * 1024)
 
 
-def _write_generated_member(zf: zipfile.ZipFile, arcname: str, text: str) -> None:
+def _write_generated_member(
+    zf: zipfile.ZipFile | PackRecord, arcname: str, text: str
+) -> None:
     """Write a pack member the builder composes rather than copies.
 
     READMEs, instruction notes and the manifest are produced at build time,
@@ -581,7 +585,7 @@ def _data_directory_members(
 
 
 def _pack_data_directories(
-    zf: zipfile.ZipFile,
+    zf: zipfile.ZipFile | PackRecord,
     pack_systems: dict,
     data_registry: dict | None,
     platform_name: str,
@@ -1476,7 +1480,9 @@ def generate_pack(
 
 
 def _extract_zip_to_archive(
-    source_zip: str, dest_prefix: str, target_zf: zipfile.ZipFile
+    source_zip: str,
+    dest_prefix: str,
+    target_zf: zipfile.ZipFile | PackRecord,
 ) -> None:
     """Extract contents of a source ZIP into target ZIP under dest_prefix."""
     with zipfile.ZipFile(source_zip, "r") as src:
@@ -1507,7 +1513,7 @@ def _extract_zip_to_archive(
 def _add_zip_to_pack(
     source_zip: str,
     dest_path: str,
-    target_zf: zipfile.ZipFile,
+    target_zf: zipfile.ZipFile | PackRecord,
     file_entry: dict | None = None,
 ) -> None:
     """Write a source ZIP into the pack, byte for byte.
@@ -1555,7 +1561,7 @@ class DamagedArchiveError(OSError):
 
 
 def _pack_data_tree(
-    zf: zipfile.ZipFile,
+    zf: zipfile.ZipFile | PackRecord,
     local_cache: str,
     dd_dest: str,
     seen_destinations: set[str],