diff --git a/Orthtree/include/CGAL/Orthtree.h b/Orthtree/include/CGAL/Orthtree.h
index 77d95c4c898..9b209bdd74f 100644
--- a/Orthtree/include/CGAL/Orthtree.h
+++ b/Orthtree/include/CGAL/Orthtree.h
@@ -15,6 +15,7 @@
 #include <CGAL/license/Orthtree.h>
 
 #include <CGAL/Orthtree/Cartesian_ranges.h>
+#include <CGAL/Orthtree/Nearest_neighbors.h>
 #include <CGAL/Orthtree/Split_predicates.h>
 #include <CGAL/Orthtree/Traversals.h>
 #include <CGAL/Orthtree/Traversal_iterator.h>