diff --git a/third_party/agg23/agg_rasterizer_scanline_aa.cpp b/third_party/agg23/agg_rasterizer_scanline_aa.cpp
index c90bdafdd..1fe9a0c32 100644
--- a/third_party/agg23/agg_rasterizer_scanline_aa.cpp
+++ b/third_party/agg23/agg_rasterizer_scanline_aa.cpp
@@ -495,4 +495,11 @@ void outline_aa::sort_cells()
     }
     m_sorted = true;
 }
+// static
+int rasterizer_scanline_aa::calculate_area(int cover, int shift)
+{
+    unsigned int result = cover;
+    result <<= shift;
+    return result;
+}
 }
diff --git a/third_party/agg23/agg_rasterizer_scanline_aa.h b/third_party/agg23/agg_rasterizer_scanline_aa.h
index c747ee379..281933710 100644
--- a/third_party/agg23/agg_rasterizer_scanline_aa.h
+++ b/third_party/agg23/agg_rasterizer_scanline_aa.h
@@ -338,7 +338,6 @@ public:
                 const cell_aa* cur_cell = *cells;
                 int x    = cur_cell->x;
                 int area = cur_cell->area;
-                unsigned alpha;
                 cover += cur_cell->cover;
                 while(--num_cells) {
                     cur_cell = *++cells;
@@ -349,14 +348,14 @@ public:
                     cover += cur_cell->cover;
                 }
                 if(area) {
-                    alpha = calculate_alpha((cover << (poly_base_shift + 1)) - area, no_smooth);
+                    unsigned alpha = calculate_alpha(calculate_area(cover, poly_base_shift + 1) - area, no_smooth);
                     if(alpha) {
                         sl.add_cell(x, alpha);
                     }
                     x++;
                 }
                 if(num_cells && cur_cell->x > x) {
-                    alpha = calculate_alpha(cover << (poly_base_shift + 1), no_smooth);
+                    unsigned alpha = calculate_alpha(calculate_area(cover, poly_base_shift + 1), no_smooth);
                     if(alpha) {
                         sl.add_span(x, cur_cell->x - x, alpha);
                     }
@@ -459,6 +458,8 @@ private:
         m_prev_y = y;
     }
 private:
+    static int calculate_area(int cover, int shift);
+
     outline_aa     m_outline;
     filling_rule_e m_filling_rule;
     int            m_clipped_start_x;