diff --git a/doc/source/basics.rst b/doc/source/basics.rst
index ec8456089f452..4d67616c5cd60 100644
--- a/doc/source/basics.rst
+++ b/doc/source/basics.rst
@@ -869,7 +869,7 @@ Aligning objects with each other with ``align``
 The ``align`` method is the fastest way to simultaneously align two objects. It
 supports a ``join`` argument (related to :ref:`joining and merging <merging>`):
 
-  - ``join='outer'``: take the union of the indexes
+  - ``join='outer'``: take the union of the indexes (default)
   - ``join='left'``: use the calling object's index
   - ``join='right'``: use the passed object's index
   - ``join='inner'``: intersect the indexes