diff --git a/Convex_hull_3/include/CGAL/Convex_hull_vertex_base_2.h b/Convex_hull_3/include/CGAL/Convex_hull_vertex_base_2.h
index a7f31124646..cef5f5eeac8 100644
--- a/Convex_hull_3/include/CGAL/Convex_hull_vertex_base_2.h
+++ b/Convex_hull_3/include/CGAL/Convex_hull_vertex_base_2.h
@@ -18,6 +18,7 @@
 #include <CGAL/license/Convex_hull_3.h>
 
 #include <CGAL/Triangulation_ds_vertex_base_2.h>
+#include <CGAL/IO/io.h>
 
 #include <iostream>
 
diff --git a/Triangulation_2/include/CGAL/Regular_triangulation_vertex_base_2.h b/Triangulation_2/include/CGAL/Regular_triangulation_vertex_base_2.h
index a2ca48dac15..cc937b133c6 100644
--- a/Triangulation_2/include/CGAL/Regular_triangulation_vertex_base_2.h
+++ b/Triangulation_2/include/CGAL/Regular_triangulation_vertex_base_2.h
@@ -16,8 +16,8 @@
 
 #include <CGAL/license/Triangulation_2.h>
 
-
 #include <CGAL/Triangulation_ds_vertex_base_2.h>
+#include <CGAL/IO/io.h>
 
 namespace CGAL {
 
diff --git a/Triangulation_2/include/CGAL/Triangulation_vertex_base_2.h b/Triangulation_2/include/CGAL/Triangulation_vertex_base_2.h
index ecbb1083689..0e2bb5e0333 100644
--- a/Triangulation_2/include/CGAL/Triangulation_vertex_base_2.h
+++ b/Triangulation_2/include/CGAL/Triangulation_vertex_base_2.h
@@ -18,6 +18,7 @@
 
 #include <CGAL/config.h>
 #include <CGAL/Triangulation_ds_vertex_base_2.h>
+#include <CGAL/IO/io.h>
 
 namespace CGAL {
 
diff --git a/Triangulation_3/include/CGAL/Regular_triangulation_vertex_base_3.h b/Triangulation_3/include/CGAL/Regular_triangulation_vertex_base_3.h
index cd697f17978..cdd1bce326b 100644
--- a/Triangulation_3/include/CGAL/Regular_triangulation_vertex_base_3.h
+++ b/Triangulation_3/include/CGAL/Regular_triangulation_vertex_base_3.h
@@ -18,6 +18,7 @@
 #include <CGAL/basic.h>
 #include <CGAL/Triangulation_vertex_base_3.h>
 #include <CGAL/Triangulation_ds_vertex_base_3.h>
+#include <CGAL/IO/io.h>
 
 namespace CGAL {
 
diff --git a/Triangulation_3/include/CGAL/Triangulation_vertex_base_3.h b/Triangulation_3/include/CGAL/Triangulation_vertex_base_3.h
index 60e11f6233e..99a589740e2 100644
--- a/Triangulation_3/include/CGAL/Triangulation_vertex_base_3.h
+++ b/Triangulation_3/include/CGAL/Triangulation_vertex_base_3.h
@@ -17,6 +17,7 @@
 
 #include <CGAL/basic.h>
 #include <CGAL/Triangulation_ds_vertex_base_3.h>
+#include <CGAL/IO/io.h>
 
 namespace CGAL {