diff --git a/src/gui/painting/qdrawhelper.cpp b/src/gui/painting/qdrawhelper.cpp
index a0f7155c67..ac22c7fc00 100644
--- a/src/gui/painting/qdrawhelper.cpp
+++ b/src/gui/painting/qdrawhelper.cpp
@@ -5754,9 +5754,9 @@ static inline void rgbBlendPixel(quint32 *dst, int coverage, int sr, int sg, int
     dg = gamma[dg];
     db = gamma[db];
 
-    int nr = qt_div_255((sr - dr) * mr) + dr;
-    int ng = qt_div_255((sg - dg) * mg) + dg;
-    int nb = qt_div_255((sb - db) * mb) + db;
+    int nr = qt_div_255(sr * mr + dr * (255 - mr));
+    int ng = qt_div_255(sg * mg + dg * (255 - mg));
+    int nb = qt_div_255(sb * mb + db * (255 - mb));
 
     nr = invgamma[nr];
     ng = invgamma[ng];
@@ -5781,9 +5781,9 @@ static inline void grayBlendPixel(quint32 *dst, int coverage, int sr, int sg, in
 
     int alpha = coverage;
     int ialpha = 255 - alpha;
-    int nr = (sr * alpha + ialpha * dr) / 255;
-    int ng = (sg * alpha + ialpha * dg) / 255;
-    int nb = (sb * alpha + ialpha * db) / 255;
+    int nr = qt_div_255(sr * alpha + dr * ialpha);
+    int ng = qt_div_255(sg * alpha + dg * ialpha);
+    int nb = qt_div_255(sb * alpha + db * ialpha);
 
     nr = invgamma[nr];
     ng = invgamma[ng];
diff --git a/src/gui/painting/qdrawhelper_p.h b/src/gui/painting/qdrawhelper_p.h
index ff98d186c5..d636eabe3f 100644
--- a/src/gui/painting/qdrawhelper_p.h
+++ b/src/gui/painting/qdrawhelper_p.h
@@ -705,6 +705,7 @@ static Q_ALWAYS_INLINE uint BYTE_MUL_RGB16_32(uint x, uint a) {
     return t;
 }
 
+// qt_div_255 is a fast rounded division by 255 using an approximation that is accurate for all positive 16-bit integers
 static Q_DECL_CONSTEXPR Q_ALWAYS_INLINE int qt_div_255(int x) { return (x + (x>>8) + 0x80) >> 8; }
 static Q_DECL_CONSTEXPR Q_ALWAYS_INLINE uint qt_div_65535(uint x) { return (x + (x>>16) + 0x8000U) >> 16; }