diff --git a/include/mapnik/graphics.hpp b/include/mapnik/graphics.hpp
index d59d25134..2ef1456e0 100644
--- a/include/mapnik/graphics.hpp
+++ b/include/mapnik/graphics.hpp
@@ -369,13 +369,12 @@ namespace mapnik
                       unsigned g0 = (rgba0 >> 16 ) & 0xff;
                       unsigned b0 = (rgba0 >> 8) & 0xff;
 
-                      unsigned a = (a1 * 255 + (255 - a1) * a0 + 127)/255;
+                      r0 = uint8_t(((r1 - r0) * a1 + (r0 << 8)) >> 8);
+                      g0 = uint8_t(((g1 - g0) * a1 + (g0 << 8)) >> 8);
+                      b0 = uint8_t(((b1 - b0) * a1 + (b0 << 8)) >> 8);
+                      a0 = uint8_t((a1 + a0) - ((a1 * a0 + 255) >> 8));
 
-                      r0 = (r1*a1 + (((255 - a1) * a0 + 127)/255) * r0 + 127)/a;
-                      g0 = (g1*a1 + (((255 - a1) * a0 + 127)/255) * g0 + 127)/a;
-                      b0 = (b1*a1 + (((255 - a1) * a0 + 127)/255) * b0 + 127)/a;
-
-                      row_to[x] = (a)| (b0 << 8) |  (g0 << 16) | (r0 << 24) ;
+                      row_to[x] = (a0)| (b0 << 8) |  (g0 << 16) | (r0 << 24) ;
 #else
                       unsigned a1 = int( ((rgba1 >> 24) & 0xff) * opacity );
                       if (a1 == 0) continue;
@@ -388,13 +387,12 @@ namespace mapnik
                       unsigned g0 = (rgba0 >> 8 ) & 0xff;
                       unsigned b0 = (rgba0 >> 16) & 0xff;
 
-                      unsigned a = (a1 * 255 + (255 - a1) * a0 + 127)/255;
-
-                      r0 = (r1*a1 + (((255 - a1) * a0 + 127)/255) * r0 + 127)/a;
-                      g0 = (g1*a1 + (((255 - a1) * a0 + 127)/255) * g0 + 127)/a;
-                      b0 = (b1*a1 + (((255 - a1) * a0 + 127)/255) * b0 + 127)/a;
-
-                      row_to[x] = (a << 24)| (b0 << 16) |  (g0 << 8) | (r0) ;
+                      r0 = uint8_t(((r1 - r0) * a1 + (r0 << 8)) >> 8);
+                      g0 = uint8_t(((g1 - g0) * a1 + (g0 << 8)) >> 8);
+                      b0 = uint8_t(((b1 - b0) * a1 + (b0 << 8)) >> 8);
+                      a0 = uint8_t((a1 + a0) - ((a1 * a0 + 255) >> 8));
+                      
+                      row_to[x] = (a0 << 24)| (b0 << 16) |  (g0 << 8) | (r0) ;
 #endif
                     }
                 }