diff --git a/doc/internals/how-to-create-custom-index.rst b/doc/internals/how-to-create-custom-index.rst
index 93805229db1..90b3412c2cb 100644
--- a/doc/internals/how-to-create-custom-index.rst
+++ b/doc/internals/how-to-create-custom-index.rst
@@ -1,5 +1,7 @@
 .. currentmodule:: xarray
 
+.. _internals.custom indexes:
+
 How to create a custom index
 ============================
 
diff --git a/doc/internals/interoperability.rst b/doc/internals/interoperability.rst
index dbfccc9b9ce..1388ceff7fc 100644
--- a/doc/internals/interoperability.rst
+++ b/doc/internals/interoperability.rst
@@ -11,7 +11,7 @@ This interoperability comes via a set of flexible abstractions into which the us
 - :ref:`Custom file backends <add_a_backend>` via the :py:class:`~xarray.backends.BackendEntrypoint` system,
 - Numpy-like :ref:`"duck" array wrapping <internals.duckarrays>`, which supports the `Python Array API Standard <https://data-apis.org/array-api/latest/>`_,
 - :ref:`Chunked distributed array computation <internals.chunkedarrays>` via the :py:class:`~xarray.core.parallelcompat.ChunkManagerEntrypoint` system,
-- Flexible :py:class:`~xarray.indexes.Index` objects for custom label-based lookups,
+- Custom :py:class:`~xarray.indexes.Index` objects for :ref:`flexible label-based lookups <internals.custom indexes>`,
 - Extending xarray objects with domain-specific methods via :ref:`custom accessors <internals.accessors>`.
 
 .. warning::