diff --git a/doc/whats_new.rst b/doc/whats_new.rst
index 999fdee7cfb88d82959a8d502fcced345584a6b1..5bfa8a6d9cbf92949a0da7bb0560d63942920ce2 100644
--- a/doc/whats_new.rst
+++ b/doc/whats_new.rst
@@ -31,6 +31,11 @@ Enhancements
      <https://github.com/scikit-learn/scikit-learn/pull/4939>`_) by `Andrea
      Esuli`_.
 
+   - Custom metrics for the :mod:`sklearn.neighbors` binary trees now have
+     fewer constraints: they must take two 1d-arrays and return a float.
+     (`#6288 <https://github.com/scikit-learn/scikit-learn/pull/6288>`_) by
+     `Jake VanderPlas`_.
+
 Bug fixes
 .........