diff --git a/Arrangement_on_surface_2/include/CGAL/Curved_kernel_via_analysis_2/gfx/Curve_renderer_2.h b/Arrangement_on_surface_2/include/CGAL/Curved_kernel_via_analysis_2/gfx/Curve_renderer_2.h
index bdd914bf270..745381dc630 100644
--- a/Arrangement_on_surface_2/include/CGAL/Curved_kernel_via_analysis_2/gfx/Curve_renderer_2.h
+++ b/Arrangement_on_surface_2/include/CGAL/Curved_kernel_via_analysis_2/gfx/Curve_renderer_2.h
@@ -238,7 +238,8 @@ private:
     typedef std::vector<int> index_vector;
 
     //! map container element's type for maintaining a list of cache instances
-    typedef std::pair<int, int> LRU_entry;
+    typedef std::pair<int, std::size_t> LRU_entry;
+
     //! LRU list used for cache switching
     typedef std::vector< LRU_entry > Cache_list;
 
@@ -256,8 +257,9 @@ public:
     //!@{
 
     //! default constructor: a curve segment is undefined
-    Curve_renderer_2() : cache_id(-1), IA_method(0), initialized(false),
-       one(1) {
+    Curve_renderer_2() :
+      cache_id(INVALID_CACHE_ID), IA_method(0), initialized(false), one(1)
+    {
         arcno = -1;
         setup(Bbox_2(-1.0, -1.0, 1.0, 1.0), 640, 480);
     }
@@ -381,9 +383,11 @@ private:
     Clip_points btm_clip, top_clip;  //! a set of bottom and top clip points
     Poly_dst_1 btm_poly, top_poly;   //! bottom and top polynomials
 
-    int cache_id;        //! index of currently used cache instance
+    std::size_t cache_id;  //! index of currently used cache instance
     Cache_list cache_list; //! list of indices of cache instances
 
+    static constexpr std::size_t INVALID_CACHE_ID = CGAL_N_CACHES;
+
     Seed_stack s_stack;      //! a stack of seed points
     Seed_point current_seed; //! current seed point
 
@@ -1192,7 +1196,7 @@ Lexit:
 
     std::reverse(rev_points.begin(), rev_points.end());
     // resize rev_points to accommodate the size of points vector
-    unsigned rsize = rev_points.size();
+    std::size_t rsize = rev_points.size();
     rev_points.resize(rsize + points.size());
     std::copy(points.begin(), points.end(), rev_points.begin() + rsize);
 }
@@ -2312,7 +2316,8 @@ void select_cache_entry(const Arc_2& arc) {
         it++;
     }
 
-    int new_id, new_entry = (it == cache_list.end());
+    std::size_t new_id;
+    bool new_entry = (it == cache_list.end());
     if(new_entry) {
         new_id = cache_list.size();
         if(new_id >= CGAL_N_CACHES) {
diff --git a/Arrangement_on_surface_2/include/CGAL/Curved_kernel_via_analysis_2/gfx/Curve_renderer_internals.h b/Arrangement_on_surface_2/include/CGAL/Curved_kernel_via_analysis_2/gfx/Curve_renderer_internals.h
index 111c28a37e2..2031b25249b 100644
--- a/Arrangement_on_surface_2/include/CGAL/Curved_kernel_via_analysis_2/gfx/Curve_renderer_internals.h
+++ b/Arrangement_on_surface_2/include/CGAL/Curved_kernel_via_analysis_2/gfx/Curve_renderer_internals.h
@@ -1028,7 +1028,7 @@ void precompute(const Polynomial_2& in) {
 }
 
 //! \brief activates the cache entry \c cache_id
-void select_cache_entry(int cache_id)
+void select_cache_entry(std::size_t cache_id)
 {
     coeffs_x = coeffs_x_ + cache_id;
     coeffs_y = coeffs_y_ + cache_id;