diff --git a/Interpolation/test/Interpolation/include/CGAL/_test_interpolation_functions_2.C b/Interpolation/test/Interpolation/include/CGAL/_test_interpolation_functions_2.cpp
similarity index 100%
rename from Interpolation/test/Interpolation/include/CGAL/_test_interpolation_functions_2.C
rename to Interpolation/test/Interpolation/include/CGAL/_test_interpolation_functions_2.cpp
diff --git a/Interpolation/test/Interpolation/include/CGAL/_test_natural_neighbors_2.C b/Interpolation/test/Interpolation/include/CGAL/_test_natural_neighbors_2.cpp
similarity index 100%
rename from Interpolation/test/Interpolation/include/CGAL/_test_natural_neighbors_2.C
rename to Interpolation/test/Interpolation/include/CGAL/_test_natural_neighbors_2.cpp
diff --git a/Interpolation/test/Interpolation/include/CGAL/_test_regular_neighbors_2.C b/Interpolation/test/Interpolation/include/CGAL/_test_regular_neighbors_2.cpp
similarity index 100%
rename from Interpolation/test/Interpolation/include/CGAL/_test_regular_neighbors_2.C
rename to Interpolation/test/Interpolation/include/CGAL/_test_regular_neighbors_2.cpp
diff --git a/Interpolation/test/Interpolation/include/CGAL/_test_surface_neighbors_3.C b/Interpolation/test/Interpolation/include/CGAL/_test_surface_neighbors_3.cpp
similarity index 100%
rename from Interpolation/test/Interpolation/include/CGAL/_test_surface_neighbors_3.C
rename to Interpolation/test/Interpolation/include/CGAL/_test_surface_neighbors_3.cpp
diff --git a/Interpolation/test/Interpolation/test_interpolation_functions_2.cpp b/Interpolation/test/Interpolation/test_interpolation_functions_2.cpp
index 454ab57509a..2f296bfcf38 100644
--- a/Interpolation/test/Interpolation/test_interpolation_functions_2.cpp
+++ b/Interpolation/test/Interpolation/test_interpolation_functions_2.cpp
@@ -23,7 +23,7 @@
 #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 #include <CGAL/Delaunay_triangulation_2.h>
 
-#include <CGAL/_test_interpolation_functions_2.C>
+#include <CGAL/_test_interpolation_functions_2.cpp>
 
 struct K : CGAL::Exact_predicates_exact_constructions_kernel {};
 typedef CGAL::Delaunay_triangulation_2<K>            Dt;
diff --git a/Interpolation/test/Interpolation/test_natural_neighbors_2.cpp b/Interpolation/test/Interpolation/test_natural_neighbors_2.cpp
index 3c2a9c03678..419e19b0edd 100644
--- a/Interpolation/test/Interpolation/test_natural_neighbors_2.cpp
+++ b/Interpolation/test/Interpolation/test_natural_neighbors_2.cpp
@@ -21,7 +21,7 @@
 #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 #include <CGAL/Delaunay_triangulation_2.h>
 
-#include <CGAL/_test_natural_neighbors_2.C>
+#include <CGAL/_test_natural_neighbors_2.cpp>
 
 
 struct K : CGAL::Exact_predicates_inexact_constructions_kernel {};
diff --git a/Interpolation/test/Interpolation/test_regular_neighbors_2.cpp b/Interpolation/test/Interpolation/test_regular_neighbors_2.cpp
index 6de9669ff63..946d4c31bf6 100644
--- a/Interpolation/test/Interpolation/test_regular_neighbors_2.cpp
+++ b/Interpolation/test/Interpolation/test_regular_neighbors_2.cpp
@@ -24,7 +24,7 @@
 #include <CGAL/Regular_triangulation_euclidean_traits_2.h>
 #include <CGAL/Regular_triangulation_2.h>
 
-#include <CGAL/_test_regular_neighbors_2.C>
+#include <CGAL/_test_regular_neighbors_2.cpp>
 
 
 struct K : CGAL::Exact_predicates_exact_constructions_kernel {};
diff --git a/Interpolation/test/Interpolation/test_surface_neighbor_3.cpp b/Interpolation/test/Interpolation/test_surface_neighbor_3.cpp
index 0f0e0fd1094..2aedcdb7394 100644
--- a/Interpolation/test/Interpolation/test_surface_neighbor_3.cpp
+++ b/Interpolation/test/Interpolation/test_surface_neighbor_3.cpp
@@ -30,7 +30,7 @@
 #include <CGAL/Triangulation_hierarchy_3.h>
 #include <CGAL/aff_transformation_tags.h>
 
-#include <CGAL/_test_surface_neighbors_3.C>
+#include <CGAL/_test_surface_neighbors_3.cpp>
 
 
 struct K : CGAL::Exact_predicates_inexact_constructions_kernel {};