2 files changed, 5 insertions, 2 deletions
diff --git a/src/plugins/platforms/windows/qwindowsbackingstore.cpp b/src/plugins/platforms/windows/qwindowsbackingstore.cpp
index dfbbe3069c..26205eb146 100644
--- a/src/plugins/platforms/windows/qwindowsbackingstore.cpp
+++ b/src/plugins/platforms/windows/qwindowsbackingstore.cpp
@@ -88,8 +88,10 @@ void QWindowsBackingStore::flush(QWindow *window, const QRegion &region,
     QWindowsWindow *rw = QWindowsWindow::baseWindowOf(window);
 
 #ifndef Q_OS_WINCE
+    const bool hasAlpha = rw->format().hasAlpha();
     const Qt::WindowFlags flags = window->flags();
-    if ((flags & Qt::FramelessWindowHint) && QWindowsWindow::setWindowLayered(rw->handle(), flags, rw->format().hasAlpha(), rw->opacity())) {
+    if ((flags & Qt::FramelessWindowHint) && QWindowsWindow::setWindowLayered(rw->handle(), flags, hasAlpha, rw->opacity()) && hasAlpha) {
+        // Windows with alpha: Use blend function to update.
         QRect r = window->frameGeometry();
         QPoint frameOffset(window->frameMargins().left(), window->frameMargins().top());
         QRect dirtyRect = br.translated(offset + frameOffset);
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index ace18ddf5b..9d87eaa110 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -250,7 +250,8 @@ static void setWindowOpacity(HWND hwnd, Qt::WindowFlags flags, bool hasAlpha, qr
     Q_UNUSED(level);
 #else
     if (QWindowsWindow::setWindowLayered(hwnd, flags, hasAlpha, level)) {
-        if (flags & Qt::FramelessWindowHint) {
+        if (hasAlpha && (flags & Qt::FramelessWindowHint)) {
+            // Windows with alpha: Use blend function to update.
             BLENDFUNCTION blend = {AC_SRC_OVER, 0, (BYTE)(255.0 * level), AC_SRC_ALPHA};
             QWindowsContext::user32dll.updateLayeredWindow(hwnd, NULL, NULL, NULL, NULL, NULL, 0, &blend, ULW_ALPHA);
         } else {