diff --git a/pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/manual.py b/pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/manual.py
index 03c5a5dd396..d605dd88b37 100644
--- a/pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/manual.py
+++ b/pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/manual.py
@@ -623,7 +623,7 @@ class HTMLConverter(BaseConverter[ManualHTMLRenderer]):
             elif bt.type == 'footnote_ref' and (id := cast(str, bt.attrs.get('id', ''))):
                 result.append(XrefTarget(id, "???", None, None, target_file))
             elif bt.type == 'inline':
-                assert bt.children
+                assert bt.children is not None
                 result += self._collect_ids(bt.children, target_file, typ, False)
             elif id := cast(str, bt.attrs.get('id', '')):
                 # anchors and examples have no titles we could use, but we'll have to put
diff --git a/pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/md.py b/pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/md.py
index f754b61b443..85513ef4869 100644
--- a/pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/md.py
+++ b/pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/md.py
@@ -458,7 +458,7 @@ def _footnote_ids(md: markdown_it.MarkdownIt) -> None:
                 token.attrs['id'] = f'{token.meta["label"]}.__back.{token.meta["subId"]}'
                 token.meta['target'] = token.meta["label"]
             elif token.type == 'inline':
-                assert token.children
+                assert token.children is not None
                 generate_ids(token.children)
 
     def footnote_ids(state: markdown_it.rules_core.StateCore) -> None: