diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_X_trapezoid.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_X_trapezoid.h
index 897f1e477fc..6f6f72a1678 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_X_trapezoid.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_X_trapezoid.h
@@ -122,7 +122,7 @@ public:
 #if defined(__SUNPRO_CC) || defined(__PGI) || defined(__INTEL_COMPILER)
   friend class Trapezoidal_decomposition_2<Traits>::Around_point_circulator;
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
-#elif defined(__GNUC__)
+#elif (__GNUC__ > 0)
 
   friend class Trapezoidal_decomposition_2<Traits>::Around_point_circulator;
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_edge.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_edge.h
index aa3087055e7..24ad3b4bf15 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_edge.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_edge.h
@@ -94,7 +94,7 @@ public:
 #ifdef CGAL_PM_FRIEND_CLASS
 #if defined(__SUNPRO_CC) || defined(__PGI) || defined(__INTEL_COMPILER)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
-#elif defined(__GNUC__)
+#elif (__GNUC__ > 0)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
 #else
   friend class In_face_iterator;
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_fictitious_vertex.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_fictitious_vertex.h
index 548070ce8be..e47760609a0 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_fictitious_vertex.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_fictitious_vertex.h
@@ -94,7 +94,7 @@ public:
 #ifdef CGAL_PM_FRIEND_CLASS
 #if defined(__SUNPRO_CC) || defined(__PGI) || defined(__INTEL_COMPILER)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
-#elif defined(__GNUC__)
+#elif (__GNUC__ > 0)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
 #else
   friend class In_face_iterator;
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_trapezoid.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_trapezoid.h
index d7d55a86846..e74b291ab06 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_trapezoid.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_trapezoid.h
@@ -91,7 +91,7 @@ public:
 #ifdef CGAL_PM_FRIEND_CLASS
 #if defined(__SUNPRO_CC) || defined(__PGI) || defined(__INTEL_COMPILER)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
-#elif defined(__GNUC__)
+#elif (__GNUC__ > 0)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
 #else
   friend class In_face_iterator;
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_vertex.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_vertex.h
index 05a416d1342..9486ddcc41d 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_vertex.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_vertex.h
@@ -96,7 +96,7 @@ public:
 #ifdef CGAL_PM_FRIEND_CLASS
 #if defined(__SUNPRO_CC) || defined(__PGI) || defined(__INTEL_COMPILER)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
-#elif defined(__GNUC__)
+#elif (__GNUC__ > 0)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
 #else
   friend class In_face_iterator;
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_edge.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_edge.h
index 5b49445fc5b..72497798323 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_edge.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_edge.h
@@ -93,7 +93,7 @@ public:
 #ifdef CGAL_PM_FRIEND_CLASS
 #if defined(__SUNPRO_CC) || defined(__PGI) || defined(__INTEL_COMPILER)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
-#elif defined(__GNUC__)
+#elif (__GNUC__ > 0)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
 #else
   friend class In_face_iterator;
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_fictitious_vertex.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_fictitious_vertex.h
index c61205c26cd..db7a89c8275 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_fictitious_vertex.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_fictitious_vertex.h
@@ -96,7 +96,7 @@ public:
 #ifdef CGAL_PM_FRIEND_CLASS
 #if defined(__SUNPRO_CC) || defined(__PGI) || defined(__INTEL_COMPILER)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
-#elif defined(__GNUC__)
+#elif (__GNUC__ > 0)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
 #else
   friend class In_face_iterator;
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_vertex.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_vertex.h
index 6a7e6c0eb05..e9dc3158554 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_vertex.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_inactive_vertex.h
@@ -92,7 +92,7 @@ public:
 #ifdef CGAL_PM_FRIEND_CLASS
 #if defined(__SUNPRO_CC) || defined(__PGI) || defined(__INTEL_COMPILER)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
-#elif defined(__GNUC__)
+#elif (__GNUC__ > 0)
   friend class Trapezoidal_decomposition_2<Traits>::In_face_iterator;
 #else
   friend class In_face_iterator;
diff --git a/Circular_kernel_2/benchmark/parser/benchmark_parser.cpp b/Circular_kernel_2/benchmark/parser/benchmark_parser.cpp
index daab78244d1..a06431e837f 100644
--- a/Circular_kernel_2/benchmark/parser/benchmark_parser.cpp
+++ b/Circular_kernel_2/benchmark/parser/benchmark_parser.cpp
@@ -232,7 +232,7 @@ union yyalloc
 /* Copy COUNT objects from FROM to TO.  The source and destination do
    not overlap.  */
 # ifndef YYCOPY
-#  if defined (__GNUC__)
+#  if (__GNUC__ > 0)
 #   define YYCOPY(To, From, Count) \
       __builtin_memcpy (To, From, (Count) * sizeof (*(From)))
 #  else
diff --git a/Installation/cmake/modules/config/support/CGAL_test_cpp_version.cpp b/Installation/cmake/modules/config/support/CGAL_test_cpp_version.cpp
index 61d55a338b9..74d1f1c0247 100644
--- a/Installation/cmake/modules/config/support/CGAL_test_cpp_version.cpp
+++ b/Installation/cmake/modules/config/support/CGAL_test_cpp_version.cpp
@@ -18,7 +18,7 @@ int main() {
 #endif
 
 #if __has_feature(cxx_thread_local) || \
-    ( defined(__GNUC__) && __cplusplus >= 201103L )
+    ( __GNUC__ > 0 && __cplusplus >= 201103L )
   return 0;
 #else
   return 1;
diff --git a/Installation/include/CGAL/config.h b/Installation/include/CGAL/config.h
index 2fff6846f8a..c406e4df1f9 100644
--- a/Installation/include/CGAL/config.h
+++ b/Installation/include/CGAL/config.h
@@ -223,7 +223,7 @@
 #define CGAL_CFG_NO_TR1_ARRAY 1
 // never use TR1
 #define CGAL_CFG_NO_TR1_TUPLE 1
-#if !defined(__GNUC__) || defined(__INTEL_COMPILER)
+#if (__GNUC__ <= 0) || defined(__INTEL_COMPILER)
 #define CGAL_CFG_NO_STATEMENT_EXPRESSIONS 1
 #endif
 #if _MSC_VER==1800
@@ -509,20 +509,20 @@ using std::max;
 #endif
 
 #if __has_feature(cxx_thread_local) || \
-    ( defined(__GNUC__) && __cplusplus >= 201103L ) || \
+    ( (__GNUC__ > 0) && __cplusplus >= 201103L ) || \
     ( _MSC_VER >= 1900 )
 // see also Installation/cmake/modules/config/support/CGAL_test_cpp_version.cpp
 #define CGAL_CAN_USE_CXX11_THREAD_LOCAL
 #endif
 
 #if (__has_include(<mutex>) && __cplusplus >= 201103L ) | \
-    ( defined(__GNUC__) && __cplusplus >= 201103L ) || \
+    ( (__GNUC__ > 0) && __cplusplus >= 201103L ) || \
     ( _MSC_VER >= 1700 )
 #define CGAL_CAN_USE_CXX11_MUTEX
 #endif
 
 #if (__has_include(<atomic>) && __cplusplus >= 201103L ) || \
-    ( defined(__GNUC__) && __cplusplus >= 201103L ) || \
+    ( (__GNUC__ > 0) && __cplusplus >= 201103L ) || \
     ( _MSC_VER >= 1700 )
 #define CGAL_CAN_USE_CXX11_ATOMIC
 #endif
diff --git a/Installation/include/CGAL/internal/deprecation_warning.h b/Installation/include/CGAL/internal/deprecation_warning.h
index f0048e25b02..0206b562974 100644
--- a/Installation/include/CGAL/internal/deprecation_warning.h
+++ b/Installation/include/CGAL/internal/deprecation_warning.h
@@ -75,7 +75,7 @@ CGAL_static_assertion_msg(false, CGAL_INTERNAL_DEPRECATED_MESSAGE);
 #elif !defined(CGAL_NO_DEPRECATION_WARNINGS) // don't trigger on NO_DEPRECATION_WARNINGS
 #  if defined(_MSC_VER) || defined(__BORLANDC__) || defined(__DMC__)
 #    pragma message (CGAL_INTERNAL_DEPRECATED_MESSAGE)
-#  elif defined(__GNUC__) || defined(__HP_aCC) || defined(__SUNPRO_CC) || defined(__IBMCPP__)
+#  elif (__GNUC__ > 0) || defined(__HP_aCC) || defined(__SUNPRO_CC) || defined(__IBMCPP__)
      // warning does not expand its arguments, issue a warning and add the message.
 #    warning "A deprecated header has been included."
 #    pragma message (CGAL_INTERNAL_DEPRECATED_MESSAGE)
diff --git a/Number_types/include/CGAL/FPU.h b/Number_types/include/CGAL/FPU.h
index 8a8cd8a5fea..e5ffa3fcd1f 100644
--- a/Number_types/include/CGAL/FPU.h
+++ b/Number_types/include/CGAL/FPU.h
@@ -172,7 +172,7 @@ inline double IA_opacify(double x)
   // Intel has a bug where -mno-sse still defines __SSE__ and __SSE2__
   // (-mno-sse2 works though), no work-around for now.
 # if defined __SSE2_MATH__ || (defined __INTEL_COMPILER && defined __SSE2__)
-#  if defined(__GNUC__)
+#  if (__GNUC__ > 0)
   // ICEs in reload/LRA with older versions.
   asm volatile ("" : "+gx"(x) );
 #  else
diff --git a/Periodic_3_triangulation_3/test/Periodic_3_triangulation_3/include/CGAL/_test_cls_periodic_3_regular_triangulation_traits_3.h b/Periodic_3_triangulation_3/test/Periodic_3_triangulation_3/include/CGAL/_test_cls_periodic_3_regular_triangulation_traits_3.h
index 61a9aaf0a80..a7297b25ee9 100644
--- a/Periodic_3_triangulation_3/test/Periodic_3_triangulation_3/include/CGAL/_test_cls_periodic_3_regular_triangulation_traits_3.h
+++ b/Periodic_3_triangulation_3/test/Periodic_3_triangulation_3/include/CGAL/_test_cls_periodic_3_regular_triangulation_traits_3.h
@@ -10,7 +10,7 @@
 // Author(s)     :  Aymeric PELLE <aymeric.pelle@sophia.inria.fr>
 //                  Mael Rouxel-Labbé
 
-#if defined(__GNUC__)
+#if (__GNUC__ > 0)
 #  pragma GCC diagnostic ignored "-Wunused-but-set-variable"
 #endif
 
diff --git a/Periodic_3_triangulation_3/test/Periodic_3_triangulation_3/include/CGAL/_test_cls_periodic_3_triangulation_traits_3.h b/Periodic_3_triangulation_3/test/Periodic_3_triangulation_3/include/CGAL/_test_cls_periodic_3_triangulation_traits_3.h
index c8ee3c576c6..fef5f500309 100644
--- a/Periodic_3_triangulation_3/test/Periodic_3_triangulation_3/include/CGAL/_test_cls_periodic_3_triangulation_traits_3.h
+++ b/Periodic_3_triangulation_3/test/Periodic_3_triangulation_3/include/CGAL/_test_cls_periodic_3_triangulation_traits_3.h
@@ -11,7 +11,7 @@
 // Author(s)     :  Mariette Yvinec <Mariette.Yvinec@sophia.inria.fr>
 //                  Manuel Caroli <Manuel.Caroli@sophia.inria.fr>
 
-#if defined(__GNUC__)
+#if (__GNUC__ > 0)
 #  pragma GCC diagnostic ignored "-Wunused-but-set-variable"
 #endif