diff --git a/Nef_3/include/CGAL/Nef_3/Vertex.h b/Nef_3/include/CGAL/Nef_3/Vertex.h
index 1e9792c009e..1064fd5ea87 100644
--- a/Nef_3/include/CGAL/Nef_3/Vertex.h
+++ b/Nef_3/include/CGAL/Nef_3/Vertex.h
@@ -26,6 +26,7 @@
 
 #include <string>
 #include <sstream>
+#include <CGAL/IO/io.h>
 #include <CGAL/IO/Verbose_ostream.h>
 #include <CGAL/Nef_3/SNC_iteration.h>