diff --git a/Mesh_3/include/CGAL/Mesh_3/Mesher_3.h b/Mesh_3/include/CGAL/Mesh_3/Mesher_3.h
index de889e42acf..2ba606c5de3 100644
--- a/Mesh_3/include/CGAL/Mesh_3/Mesher_3.h
+++ b/Mesh_3/include/CGAL/Mesh_3/Mesher_3.h
@@ -45,6 +45,7 @@
 #include <CGAL/Mesher_level_visitors.h>
 #include <CGAL/Kernel_traits.h>
 #include <CGAL/point_generators_3.h>
+#include <CGAL/assertions.h>
 
 #ifdef CGAL_MESH_3_USE_OLD_SURFACE_RESTRICTED_DELAUNAY_UPDATE
 #include <CGAL/Surface_mesher/Surface_mesher_visitor.h>
@@ -765,6 +766,18 @@ initialize()
     facets_mesher_.scan_triangulation();
     refinement_stage = REFINE_FACETS;
   }
+
+  if (r_c3t3_.number_of_facets() == 0)
+  {
+    CGAL::warning_fail("r_c3t3_.number_of_facets() == 0",
+      __FILE__,
+      __LINE__,
+      "Warning : The mesh refinement process can't start.\n"
+      "When calling refine_mesh_3(), the input `c3t3` should have been initialized and have "
+      "at least one facet in the complex. Try to solve this issue using :\n"
+      "\t- The automatic initialization provided by make_mesh_3()\n"
+      "\t- Adding more and better chosen points on the input surface\n");
+  }
 }
 
 
diff --git a/STL_Extension/include/CGAL/assertions_impl.h b/STL_Extension/include/CGAL/assertions_impl.h
index cfe4a27cf00..8701e67ccf7 100644
--- a/STL_Extension/include/CGAL/assertions_impl.h
+++ b/STL_Extension/include/CGAL/assertions_impl.h
@@ -14,6 +14,9 @@
 //
 // Author(s)     : Geert-Jan Giezeman and Sven Schönherr
 
+#ifndef CGAL_ASSERTIONS_IMPL_H
+#define CGAL_ASSERTIONS_IMPL_H
+
 #ifdef CGAL_HEADER_ONLY
 #define CGAL_INLINE_FUNCTION inline
 #else
@@ -280,3 +283,5 @@ set_warning_behaviour(Failure_behaviour eb)
 }
 
 } //namespace CGAL
+
+#endif //CGAL_ASSERTIONS_IMPL_H