diff --git a/Mesh_2/include/CGAL/IO/write_VTU.h b/Mesh_2/include/CGAL/IO/write_VTU.h
index 9b193000418..e965633b05a 100644
--- a/Mesh_2/include/CGAL/IO/write_VTU.h
+++ b/Mesh_2/include/CGAL/IO/write_VTU.h
@@ -304,7 +304,7 @@ template <class CDT>
 void write_VTU_with_attributes(std::ostream& os,
                const CDT& tr,
                std::vector<std::pair<const char*, const std::vector<double>*> >& attributes,
-               IO::Mode mode = BINARY)
+               Mode mode = BINARY)
 {
   typedef typename CDT::Vertex_handle Vertex_handle;
   std::map<Vertex_handle, std::size_t> V;
diff --git a/Point_set_processing_3/include/CGAL/IO/read_ply_points.h b/Point_set_processing_3/include/CGAL/IO/read_ply_points.h
index 020d2bfae99..76d88a2129c 100644
--- a/Point_set_processing_3/include/CGAL/IO/read_ply_points.h
+++ b/Point_set_processing_3/include/CGAL/IO/read_ply_points.h
@@ -150,7 +150,7 @@ bool read_PLY_with_properties(std::istream& is,
   if(!is)
     return false;
 
-  IO::internal::PLY_reader reader(true);
+  internal::PLY_reader reader(true);
 
   if(!(reader.init(is)))
   {
@@ -160,13 +160,13 @@ bool read_PLY_with_properties(std::istream& is,
 
   for(std::size_t i = 0; i < reader.number_of_elements(); ++ i)
   {
-    IO::internal::PLY_element& element = reader.element(i);
+    internal::PLY_element& element = reader.element(i);
 
     for(std::size_t j = 0; j < element.number_of_items(); ++ j)
     {
       for(std::size_t k = 0; k < element.number_of_properties(); ++ k)
       {
-        IO::internal::PLY_read_number* property = element.property(k);
+        internal::PLY_read_number* property = element.property(k);
         property->get(is);
 
         if(is.fail())
@@ -176,7 +176,7 @@ bool read_PLY_with_properties(std::istream& is,
       if(element.name() == "vertex" || element.name() == "vertices")
       {
         OutputValueType new_element;
-        IO::internal::process_properties(element, new_element, std::forward<PropertyHandler>(properties)...);
+        internal::process_properties(element, new_element, std::forward<PropertyHandler>(properties)...);
         *(output ++) = new_element;
       }
     }
diff --git a/Point_set_processing_3/include/CGAL/IO/read_points.h b/Point_set_processing_3/include/CGAL/IO/read_points.h
index 6dec414fccc..b9c31d64f69 100644
--- a/Point_set_processing_3/include/CGAL/IO/read_points.h
+++ b/Point_set_processing_3/include/CGAL/IO/read_points.h
@@ -90,7 +90,7 @@ bool read_points(const std::string& fname,
                  PointOutputIterator output,
                  const NamedParameters& np)
 {
-  const std::string ext = IO::internal::get_file_extension(fname);
+  const std::string ext = internal::get_file_extension(fname);
 
   if(ext == "xyz" || ext == "pwn")
     return read_XYZ<OutputIteratorValueType>(fname, output, np);
diff --git a/Point_set_processing_3/include/CGAL/IO/write_ply_points.h b/Point_set_processing_3/include/CGAL/IO/write_ply_points.h
index 196a36b6fc5..881585449e1 100644
--- a/Point_set_processing_3/include/CGAL/IO/write_ply_points.h
+++ b/Point_set_processing_3/include/CGAL/IO/write_ply_points.h
@@ -129,13 +129,13 @@ template <typename PointRange,
      << "comment Generated by the CGAL library" << std::endl
      << "element vertex " << points.size() << std::endl;
 
-  IO::internal::output_property_header (os, std::forward<PropertyHandler>(properties)...);
+  internal::output_property_header (os, std::forward<PropertyHandler>(properties)...);
 
   os << "end_header" << std::endl;
 
   // Write positions + normals
   for(typename PointRange::const_iterator it = points.begin(); it != points.end(); it++)
-    IO::internal::output_properties (os, it, std::forward<PropertyHandler>(properties)...);
+    internal::output_properties (os, it, std::forward<PropertyHandler>(properties)...);
 
   return !os.fail();
 }
diff --git a/Point_set_processing_3/include/CGAL/IO/write_points.h b/Point_set_processing_3/include/CGAL/IO/write_points.h
index faccb3b08b1..61d64bfe8b1 100644
--- a/Point_set_processing_3/include/CGAL/IO/write_points.h
+++ b/Point_set_processing_3/include/CGAL/IO/write_points.h
@@ -102,7 +102,7 @@ bool write_points(const std::string& fname,
 #endif
                   )
 {
-  const std::string ext = IO::internal::get_file_extension(fname);
+  const std::string ext = internal::get_file_extension(fname);
 
   if(ext == "xyz" || ext == "pwn")
     return write_XYZ(fname, points, np);
diff --git a/Stream_support/include/CGAL/IO/GOCAD.h b/Stream_support/include/CGAL/IO/GOCAD.h
index ab838f15b9e..325fa2cacf2 100644
--- a/Stream_support/include/CGAL/IO/GOCAD.h
+++ b/Stream_support/include/CGAL/IO/GOCAD.h
@@ -376,7 +376,7 @@ bool write_GOCAD(std::ostream& os,
 #endif
                  )
 {
-  return IO::internal::write_GOCAD(os, "anonymous", points, polygons, np);
+  return internal::write_GOCAD(os, "anonymous", points, polygons, np);
 }
 
 /// \cond SKIP_IN_MANUAL
@@ -385,7 +385,7 @@ template <typename PointRange, typename PolygonRange>
 bool write_GOCAD(std::ostream& os, const PointRange& points, const PolygonRange& polygons,
                  typename boost::enable_if<internal::is_Range<PolygonRange> >::type* = nullptr)
 {
-  return IO::internal::write_GOCAD(os, "anonymous", points, polygons, parameters::all_default());
+  return internal::write_GOCAD(os, "anonymous", points, polygons, parameters::all_default());
 }
 
 /// \endcond
@@ -431,7 +431,7 @@ bool write_GOCAD(const std::string& fname,
 {
   std::ofstream os(fname);
   CGAL::set_mode(os, CGAL::IO::ASCII);
-  return IO::internal::write_GOCAD(os, fname.c_str(), points, polygons, np);
+  return internal::write_GOCAD(os, fname.c_str(), points, polygons, np);
 }
 
 /// \cond SKIP_IN_MANUAL