diff --git a/src/gui/painting/qblendfunctions.cpp b/src/gui/painting/qblendfunctions.cpp
index 0a5d458532d..a4a091a29f9 100644
--- a/src/gui/painting/qblendfunctions.cpp
+++ b/src/gui/painting/qblendfunctions.cpp
@@ -385,19 +385,25 @@ void qt_blend_rgb32_on_rgb32(uchar *destPixels, int dbpl,
             destPixels, dbpl, srcPixels, sbpl, w, h, const_alpha);
     fflush(stdout);
 #endif
-
-    if (const_alpha != 256) {
-        qt_blend_argb32_on_argb32(destPixels, dbpl, srcPixels, sbpl, w, h, const_alpha);
-        return;
-    }
-
     const uint *src = (const uint *) srcPixels;
     uint *dst = (uint *) destPixels;
-    int len = w * 4;
-    for (int y=0; y<h; ++y) {
-        memcpy(dst, src, len);
-        dst = (quint32 *)(((uchar *) dst) + dbpl);
-        src = (const quint32 *)(((const uchar *) src) + sbpl);
+    if (const_alpha == 256) {
+        const int len = w * 4;
+        for (int y = 0; y < h; ++y) {
+            memcpy(dst, src, len);
+            dst = (quint32 *)(((uchar *) dst) + dbpl);
+            src = (const quint32 *)(((const uchar *) src) + sbpl);
+        }
+        return;
+    } else if (const_alpha != 0) {
+        const_alpha = (const_alpha * 255) >> 8;
+        int ialpha = 255 - const_alpha;
+        for (int y=0; y<h; ++y) {
+            for (int x=0; x<w; ++x)
+                dst[x] = INTERPOLATE_PIXEL_255(dst[x], ialpha, src[x], const_alpha);
+            dst = (quint32 *)(((uchar *) dst) + dbpl);
+            src = (const quint32 *)(((const uchar *) src) + sbpl);
+        }
     }
 }
 
@@ -414,7 +420,7 @@ struct Blend_RGB32_on_RGB32_ConstAlpha {
     }
 
     inline void write(quint32 *dst, quint32 src) {
-        *dst = BYTE_MUL(src, m_alpha) + BYTE_MUL(*dst, m_ialpha);
+        *dst = INTERPOLATE_PIXEL_255(src, m_alpha, *dst, m_ialpha);
     }
 
     inline void flush(void *) {}
diff --git a/src/gui/painting/qdrawhelper_avx2.cpp b/src/gui/painting/qdrawhelper_avx2.cpp
index acc9bc7ba1a..9c1335298eb 100644
--- a/src/gui/painting/qdrawhelper_avx2.cpp
+++ b/src/gui/painting/qdrawhelper_avx2.cpp
@@ -267,11 +267,9 @@ void qt_blend_rgb32_on_rgb32_avx2(uchar *destPixels, int dbpl,
         // 2) interpolate pixels with AVX2
         for (; x < (w - 7); x += 8) {
             const __m256i srcVector = _mm256_lddqu_si256((const __m256i *)&src[x]);
-            if (!_mm256_testz_si256(srcVector, srcVector)) {
-                __m256i dstVector = _mm256_load_si256((__m256i *)&dst[x]);
-                INTERPOLATE_PIXEL_255_AVX2(srcVector, dstVector, constAlphaVector, oneMinusConstAlpha, colorMask, half);
-                _mm256_store_si256((__m256i *)&dst[x], dstVector);
-            }
+            __m256i dstVector = _mm256_load_si256((__m256i *)&dst[x]);
+            INTERPOLATE_PIXEL_255_AVX2(srcVector, dstVector, constAlphaVector, oneMinusConstAlpha, colorMask, half);
+            _mm256_store_si256((__m256i *)&dst[x], dstVector);
         }
 
         // 3) Epilogue
diff --git a/src/gui/painting/qdrawhelper_neon.cpp b/src/gui/painting/qdrawhelper_neon.cpp
index d51b43961c5..a833520b006 100644
--- a/src/gui/painting/qdrawhelper_neon.cpp
+++ b/src/gui/painting/qdrawhelper_neon.cpp
@@ -523,8 +523,6 @@ void qt_blend_rgb32_on_rgb32_neon(uchar *destPixels, int dbpl,
                     vst1q_u32((uint32_t *)&dst[x], vcombine_u32(result32_low, result32_high));
                 }
                 for (; x<w; ++x) {
-                    uint s = src[x];
-                    s = BYTE_MUL(s, const_alpha);
                     dst[x] = INTERPOLATE_PIXEL_255(src[x], const_alpha, dst[x], one_minus_const_alpha);
                 }
                 dst = (quint32 *)(((uchar *) dst) + dbpl);
diff --git a/src/gui/painting/qdrawhelper_sse2.cpp b/src/gui/painting/qdrawhelper_sse2.cpp
index 5ff08e81536..edce70d2d0b 100644
--- a/src/gui/painting/qdrawhelper_sse2.cpp
+++ b/src/gui/painting/qdrawhelper_sse2.cpp
@@ -101,7 +101,6 @@ void qt_blend_rgb32_on_rgb32_sse2(uchar *destPixels, int dbpl,
     quint32 *dst = (quint32 *) destPixels;
     if (const_alpha != 256) {
         if (const_alpha != 0) {
-            const __m128i nullVector = _mm_set1_epi32(0);
             const __m128i half = _mm_set1_epi16(0x80);
             const __m128i colorMask = _mm_set1_epi32(0x00ff00ff);
 
@@ -119,12 +118,10 @@ void qt_blend_rgb32_on_rgb32_sse2(uchar *destPixels, int dbpl,
 
                 for (; x < w-3; x += 4) {
                     __m128i srcVector = _mm_loadu_si128((const __m128i *)&src[x]);
-                    if (_mm_movemask_epi8(_mm_cmpeq_epi32(srcVector, nullVector)) != 0xffff) {
-                        const __m128i dstVector = _mm_load_si128((__m128i *)&dst[x]);
-                        __m128i result;
-                        INTERPOLATE_PIXEL_255_SSE2(result, srcVector, dstVector, constAlphaVector, oneMinusConstAlpha, colorMask, half);
-                        _mm_store_si128((__m128i *)&dst[x], result);
-                    }
+                    const __m128i dstVector = _mm_load_si128((__m128i *)&dst[x]);
+                    __m128i result;
+                    INTERPOLATE_PIXEL_255_SSE2(result, srcVector, dstVector, constAlphaVector, oneMinusConstAlpha, colorMask, half);
+                    _mm_store_si128((__m128i *)&dst[x], result);
                 }
                 SIMD_EPILOGUE(x, w, 3)
                     dst[x] = INTERPOLATE_PIXEL_255(src[x], const_alpha, dst[x], one_minus_const_alpha);
diff --git a/tests/auto/gui/painting/qpainter/tst_qpainter.cpp b/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
index 254ab1f8ad3..c729b2f94c8 100644
--- a/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
+++ b/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
@@ -300,6 +300,8 @@ private slots:
 
     void QTBUG56252();
 
+    void blendNullRGB32();
+
 private:
     void fillData();
     void setPenColor(QPainter& p);
@@ -5139,6 +5141,24 @@ void tst_QPainter::QTBUG56252()
     // If no crash or illegal memory read, all is fine
 }
 
+void tst_QPainter::blendNullRGB32()
+{
+    quint32 data[16] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+
+    QImage nullImage((const uchar*)data, 16, 1,  QImage::Format_RGB32);
+    QImage image(16, 1, QImage::Format_RGB32);
+    image.fill(Qt::white);
+
+    QPainter paint(&image);
+    paint.setCompositionMode(QPainter::CompositionMode_Source);
+    paint.setOpacity(0.5);
+    paint.drawImage(0, 0, nullImage);
+    paint.end();
+
+    for (int i=0; i < image.width(); ++i)
+        QVERIFY(image.pixel(i,0) != 0xffffffff);
+}
+
 QTEST_MAIN(tst_QPainter)
 
 #include "tst_qpainter.moc"