diff --git a/CHANGELOG b/CHANGELOG
index f0352cbe..07693981 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -16,6 +16,7 @@ This release introduces several bug fixes and minor improvements.
     - [spatialPartitioning] Simplify node customization (#128)
     - [fitting] Mark `Base` type as protected instead of private in CRTP classes (#119)
     - [fitting] Improve KdTreeNodes API by hiding internal memory layout, improve methods naming (#120)
+    - [SpatialPartitioning] Change part of the kdtree API (#123)
 
 - Examples
     - Fix example cuda/ponca_ssgls (#109)
diff --git a/Ponca/src/SpatialPartitioning/KdTree/kdTree.h b/Ponca/src/SpatialPartitioning/KdTree/kdTree.h
index a91f7cf4..c791bc99 100644
--- a/Ponca/src/SpatialPartitioning/KdTree/kdTree.h
+++ b/Ponca/src/SpatialPartitioning/KdTree/kdTree.h
@@ -298,7 +298,7 @@ public :
 } // namespace Ponca
 
 template <typename Traits>
-std::ostream& operator<<(std::ostream& os, Ponca::KdTreeBase<Traits>& kdtree)
+std::ostream& operator<<(std::ostream& os, const Ponca::KdTreeBase<Traits>& kdtree)
 {
     kdtree.print(os);
     return os;