diff --git a/doc/manual/substitute.py b/doc/manual/substitute.py
index d14c4ca13..eda97b252 100755
--- a/doc/manual/substitute.py
+++ b/doc/manual/substitute.py
@@ -71,7 +71,11 @@ def do_include(content: str, relative_md_path: Path, source_root: Path, search_p
 def recursive_replace(data, book_root, search_path):
     match data:
         # XXX FUTURE: drop sections once mdBook is at 0.5.0 or above in nixpkgs
-        case {'sections': items} | {'items': items}:
+        case {'sections': sections}:
+            return data | dict(
+                sections = [recursive_replace(section, book_root, search_path) for section in sections],
+            )
+        case {'items': items}:
             return data | dict(
                 items = [recursive_replace(item, book_root, search_path) for item in items],
             )