diff --git a/Kernel_d/include/CGAL/Kernel_d/Segment_d.h b/Kernel_d/include/CGAL/Kernel_d/Segment_d.h
index 5a399babf4d..bd30d04f3a7 100644
--- a/Kernel_d/include/CGAL/Kernel_d/Segment_d.h
+++ b/Kernel_d/include/CGAL/Kernel_d/Segment_d.h
@@ -19,7 +19,6 @@
 
 #include <CGAL/Kernel_d/Pair_d.h>
 #include <CGAL/Kernel_d/Point_d.h>
-#include <CGAL/Kernel_d/Segment_d.h>
 #include <CGAL/Kernel_d/Line_d.h>
 #include <CGAL/Kernel_d/Ray_d.h>
 #include <CGAL/Kernel_d/Aff_transformation_d.h>
diff --git a/Number_types/include/CGAL/CORE_BigFloat.h b/Number_types/include/CGAL/CORE_BigFloat.h
index ffefaecb748..812036e3aa6 100644
--- a/Number_types/include/CGAL/CORE_BigFloat.h
+++ b/Number_types/include/CGAL/CORE_BigFloat.h
@@ -16,7 +16,6 @@
 
 #include <CGAL/basic.h>
 #include <CGAL/number_type_basic.h>
-#include <CGAL/CORE/BigFloat.h>
 #include <CGAL/CORE_coercion_traits.h>
 #include <CGAL/Interval_traits.h>
 #include <CGAL/Bigfloat_interval_traits.h>
@@ -513,7 +512,6 @@ template <> class Real_embeddable_traits< CORE::BigFloat >
 #include <CGAL/CORE_Expr.h>
 #include <CGAL/CORE_BigInt.h>
 #include <CGAL/CORE_BigRat.h>
-#include <CGAL/CORE_BigFloat.h>
 #include <CGAL/CORE_arithmetic_kernel.h>
 
 namespace Eigen {
diff --git a/Number_types/include/CGAL/CORE_BigInt.h b/Number_types/include/CGAL/CORE_BigInt.h
index a069a4948cd..0b599543164 100644
--- a/Number_types/include/CGAL/CORE_BigInt.h
+++ b/Number_types/include/CGAL/CORE_BigInt.h
@@ -18,7 +18,6 @@
 
 #include <CGAL/config.h>
 #include <CGAL/number_type_basic.h>
-#include <CGAL/CORE/BigInt.h>
 #include <CGAL/CORE/Expr.h>
 #include <CGAL/CORE_coercion_traits.h>
 
@@ -189,7 +188,6 @@ public:
 
 //since types are included by CORE_coercion_traits.h:
 #include <CGAL/CORE_Expr.h>
-#include <CGAL/CORE_BigInt.h>
 #include <CGAL/CORE_BigRat.h>
 #include <CGAL/CORE_BigFloat.h>
 #include <CGAL/CORE_arithmetic_kernel.h>
diff --git a/Number_types/include/CGAL/CORE_BigRat.h b/Number_types/include/CGAL/CORE_BigRat.h
index 0f51dac5663..caf9b73886e 100644
--- a/Number_types/include/CGAL/CORE_BigRat.h
+++ b/Number_types/include/CGAL/CORE_BigRat.h
@@ -18,7 +18,6 @@
 
 #include <CGAL/config.h>
 #include <CGAL/number_type_basic.h>
-#include <CGAL/CORE/BigRat.h>
 #include <CGAL/CORE_coercion_traits.h>
 #include <CGAL/CORE_Expr.h> // used for To_interval-functor
 
@@ -226,7 +225,6 @@ public:
 //since types are included by CORE_coercion_traits.h:
 #include <CGAL/CORE_Expr.h>
 #include <CGAL/CORE_BigInt.h>
-#include <CGAL/CORE_BigRat.h>
 #include <CGAL/CORE_BigFloat.h>
 #include <CGAL/CORE_arithmetic_kernel.h>
 
diff --git a/Number_types/include/CGAL/CORE_Expr.h b/Number_types/include/CGAL/CORE_Expr.h
index 27491b01a85..4b720bc126b 100644
--- a/Number_types/include/CGAL/CORE_Expr.h
+++ b/Number_types/include/CGAL/CORE_Expr.h
@@ -21,7 +21,6 @@
 
 #include <CGAL/number_type_basic.h>
 #include <CGAL/CORE_coercion_traits.h>
-#include <CGAL/CORE/Expr.h>
 #include <utility>
 
 
@@ -177,7 +176,6 @@ template <> class Real_embeddable_traits< CORE::Expr >
 } //namespace CGAL
 
 //since types are included by CORE_coercion_traits.h:
-#include <CGAL/CORE_Expr.h>
 #include <CGAL/CORE_BigInt.h>
 #include <CGAL/CORE_BigRat.h>
 #include <CGAL/CORE_BigFloat.h>
diff --git a/Number_types/include/CGAL/Gmpq.h b/Number_types/include/CGAL/Gmpq.h
index 87d240ecef6..9816d719b19 100644
--- a/Number_types/include/CGAL/Gmpq.h
+++ b/Number_types/include/CGAL/Gmpq.h
@@ -209,7 +209,6 @@ namespace Eigen {
 
 //since types are included by Gmp_coercion_traits.h:
 #include <CGAL/Gmpz.h>
-#include <CGAL/Gmpq.h>
 #include <CGAL/Gmpzf.h>
 #include <CGAL/GMP_arithmetic_kernel.h>
 
diff --git a/Number_types/include/CGAL/Gmpz.h b/Number_types/include/CGAL/Gmpz.h
index c67035a1e03..63be45e78fd 100644
--- a/Number_types/include/CGAL/Gmpz.h
+++ b/Number_types/include/CGAL/Gmpz.h
@@ -241,7 +241,6 @@ namespace Eigen {
 
 
 //since types are included by Gmp_coercion_traits.h:
-#include <CGAL/Gmpz.h>
 #include <CGAL/Gmpq.h>
 #include <CGAL/Gmpzf.h>
 #include <CGAL/GMP_arithmetic_kernel.h>
diff --git a/Number_types/include/CGAL/Gmpzf.h b/Number_types/include/CGAL/Gmpzf.h
index 5b6a0448eb6..128d0f94d36 100644
--- a/Number_types/include/CGAL/Gmpzf.h
+++ b/Number_types/include/CGAL/Gmpzf.h
@@ -171,7 +171,6 @@ public:
 //since types are included by Gmp_coercion_traits.h:
 #include <CGAL/Gmpz.h>
 #include <CGAL/Gmpq.h>
-#include <CGAL/Gmpzf.h>
 
 #endif // CGAL_GMPZF_H
 
diff --git a/Skin_surface_3/include/CGAL/make_union_of_balls_3.h b/Skin_surface_3/include/CGAL/make_union_of_balls_3.h
index 6f0e242e2c1..e40ecd76707 100644
--- a/Skin_surface_3/include/CGAL/make_union_of_balls_3.h
+++ b/Skin_surface_3/include/CGAL/make_union_of_balls_3.h
@@ -20,8 +20,6 @@
 #include <CGAL/mesh_union_of_balls_3.h>
 #include <CGAL/subdivide_union_of_balls_mesh_3.h>
 
-#include <CGAL/make_union_of_balls_3.h>
-
 namespace CGAL {
 
 template <class WP_iterator, class Polyhedron_3>