diff --git a/src/gui/painting/qrgba64.h b/src/gui/painting/qrgba64.h
index fab9506..575d649 100644
--- a/src/gui/painting/qrgba64.h
+++ b/src/gui/painting/qrgba64.h
@@ -122,9 +122,21 @@ public:
     Q_DECL_CONSTEXPR quint8 green8() const { return div_257(green()); }
     Q_DECL_CONSTEXPR quint8 blue8()  const { return div_257(blue()); }
     Q_DECL_CONSTEXPR quint8 alpha8() const { return div_257(alpha()); }
-    Q_DECL_CONSTEXPR uint toArgb32() const
+    Q_DECL_RELAXED_CONSTEXPR uint toArgb32() const
     {
-        return (alpha8() << 24) | (red8() << 16) | (green8() << 8) | blue8();
+        Q_CONSTEXPR quint64 mask = Q_UINT64_C(0x0000ffff0000ffff);
+        Q_CONSTEXPR quint64 round = Q_UINT64_C(0x0000008000000080);
+        quint64 ga = (rgba >> 16) & mask;
+        quint64 rb = rgba & mask;
+        ga += round;
+        rb += round;
+        ga -= ga >> 8;
+        rb -= rb >> 8;
+        uint a = (ga >> 16) & 0xff000000;
+        uint g = ga & 0x0000ff00;
+        uint r = (rb << 8) & 0x00ff0000;
+        uint b = rb >> 40;
+        return a | r | g | b;
     }
     Q_DECL_CONSTEXPR ushort toRgb16() const
     {