diff --git a/Installation/include/CGAL/Mesh_3/Mesh_complex_3_in_triangulation_3_fwd.h b/Installation/include/CGAL/Mesh_3/Mesh_complex_3_in_triangulation_3_fwd.h
new file mode 100644
index 00000000000..2f4705e66d0
--- /dev/null
+++ b/Installation/include/CGAL/Mesh_3/Mesh_complex_3_in_triangulation_3_fwd.h
@@ -0,0 +1,34 @@
+// Copyright (C) 2020  GeometryFactory Sarl
+//
+// This file is part of CGAL (www.cgal.org)
+//
+// $URL$
+// $Id$
+// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
+//
+
+#ifndef CGAL_MESH_3_MESH_COMPLEX_3_IN_TRIANGULATION_3_FWD_H
+#define CGAL_MESH_3_MESH_COMPLEX_3_IN_TRIANGULATION_3_FWD_H
+
+/// \file Mesh_complex_3_in_triangulation_3_fwd.h
+/// Forward declarations of the Mesh_3 package.
+
+#ifndef DOXYGEN_RUNNING
+namespace CGAL {
+
+// fwdS for the public interface
+template <typename Tr,
+          typename CornerIndex = int,
+          typename CurveIndex = int>
+class Mesh_complex_3_in_triangulation_3;
+
+template<class Tr, bool c3t3_loader_failed>
+bool build_triangulation_from_file(std::istream& is,
+                                   Tr& tr);
+
+} // CGAL
+#endif
+
+#endif /* CGAL_MESH_3_MESH_COMPLEX_3_IN_TRIANGULATION_3_FWD_H */
+
+
diff --git a/Mesh_3/include/CGAL/IO/File_medit.h b/Mesh_3/include/CGAL/IO/File_medit.h
index 99109faebec..d8b949fb2c7 100644
--- a/Mesh_3/include/CGAL/IO/File_medit.h
+++ b/Mesh_3/include/CGAL/IO/File_medit.h
@@ -17,6 +17,7 @@
 #include <CGAL/license/Triangulation_3.h>
 
 #include <CGAL/Mesh_3/config.h>
+#include <CGAL/Mesh_3/Mesh_complex_3_in_triangulation_3_fwd.h>
 
 #include <CGAL/utility.h>
 #include <CGAL/basic.h>
diff --git a/Mesh_3/include/CGAL/Mesh_complex_3_in_triangulation_3.h b/Mesh_3/include/CGAL/Mesh_complex_3_in_triangulation_3.h
index 5440b0c0d52..0eb11a1f3c6 100644
--- a/Mesh_3/include/CGAL/Mesh_complex_3_in_triangulation_3.h
+++ b/Mesh_3/include/CGAL/Mesh_complex_3_in_triangulation_3.h
@@ -20,6 +20,7 @@
 
 #include <CGAL/license/Triangulation_3.h>
 
+#include <CGAL/Mesh_3/Mesh_complex_3_in_triangulation_3_fwd.h>
 #include <CGAL/disable_warnings.h>
 #include <CGAL/iterator.h>
 #include <CGAL/Mesh_3/utilities.h>
@@ -38,8 +39,8 @@ namespace CGAL {
 
 
 template <typename Tr,
-          typename CornerIndex = int,
-          typename CurveIndex = int>
+          typename CornerIndex,
+          typename CurveIndex>
 class Mesh_complex_3_in_triangulation_3 :
   public Mesh_3::Mesh_complex_3_in_triangulation_3_base<
     Tr, typename Tr::Concurrency_tag>