diff --git a/_delb/utils.py b/_delb/utils.py
index 4fcd1ce..7482380 100644
--- a/_delb/utils.py
+++ b/_delb/utils.py
@@ -361,7 +361,7 @@ def _random_unused_prefix(namespaces: etree._NSMap) -> str:
     )
 
 
-def sort_nodes_in_document_order(nodes: Iterable[NodeBase]) -> Iterator[NodeBase]:
+def _sort_nodes_in_document_order(nodes: Iterable[NodeBase]) -> Iterator[NodeBase]:
     node_index_cache: dict[int, int] = {}
     sorter = _NodesSorter()
     for node in nodes:
@@ -429,5 +429,5 @@ def traverse_df_ltr_ttb(root: NodeBase, *filters: Filter) -> Iterator[NodeBase]:
     first.__name__,
     get_traverser.__name__,
     last.__name__,
-    sort_nodes_in_document_order.__name__,
+    _sort_nodes_in_document_order.__name__,
 )
diff --git a/_delb/xpath/__init__.py b/_delb/xpath/__init__.py
index 13acc5b..51aef44 100644
--- a/_delb/xpath/__init__.py
+++ b/_delb/xpath/__init__.py
@@ -72,7 +72,7 @@
 from cssselect import GenericTranslator
 
 from _delb.names import Namespaces
-from _delb.utils import sort_nodes_in_document_order
+from _delb.utils import _sort_nodes_in_document_order
 from _delb.xpath.ast import EvaluationContext
 from _delb.xpath import functions  # noqa: F401
 from _delb.xpath.parser import parse
@@ -141,7 +141,7 @@ def in_document_order(self) -> QueryResults:
         Returns another :class:`QueryResults` instance where the contained nodes are
         sorted in document order.
         """
-        return QueryResults(sort_nodes_in_document_order(self))
+        return QueryResults(_sort_nodes_in_document_order(self))
 
     @property
     def last(self) -> Optional[NodeBase]: