diff --git a/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp b/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp
index 1abd6808bbc..a0265bdc338 100644
--- a/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp
+++ b/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp
@@ -283,7 +283,9 @@ QWaylandShmBuffer *QWaylandShmBackingStore::getBuffer(const QSize &size, bool &b
         return buffer;
 
     if (mBuffers.size() < MAX_BUFFERS) {
-        QImage::Format format = QPlatformScreen::platformScreenForWindow(window())->format();
+        QImage::Format format = QImage::Format_ARGB32_Premultiplied;
+        if (!waylandWindow()->format().hasAlpha())
+            format = QImage::Format_RGB32;
         QWaylandShmBuffer *b = new QWaylandShmBuffer(mDisplay, size, format, waylandWindow()->scale());
         bufferWasRecreated = true;
         mBuffers.push_front(b);
diff --git a/src/plugins/platforms/wayland/qwaylandshmwindow.cpp b/src/plugins/platforms/wayland/qwaylandshmwindow.cpp
index 8fecad178bd..10c90d1c157 100644
--- a/src/plugins/platforms/wayland/qwaylandshmwindow.cpp
+++ b/src/plugins/platforms/wayland/qwaylandshmwindow.cpp
@@ -14,6 +14,12 @@ namespace QtWaylandClient {
 QWaylandShmWindow::QWaylandShmWindow(QWindow *window, QWaylandDisplay *display)
     : QWaylandWindow(window, display)
 {
+    mSurfaceFormat.setRedBufferSize(8);
+    mSurfaceFormat.setGreenBufferSize(8);
+    mSurfaceFormat.setBlueBufferSize(8);
+
+    const QSurfaceFormat format = window->requestedFormat();
+    mSurfaceFormat.setAlphaBufferSize(format.hasAlpha() ? 8 : 0);
 }
 
 QWaylandShmWindow::~QWaylandShmWindow()
@@ -25,6 +31,15 @@ QWaylandWindow::WindowType QWaylandShmWindow::windowType() const
     return QWaylandWindow::Shm;
 }
 
+void QWaylandShmWindow::setWindowFlags(Qt::WindowFlags flags)
+{
+    QWaylandWindow::setWindowFlags(flags);
+
+    const QSurfaceFormat format = window()->requestedFormat();
+    if (!format.hasAlpha())
+        mSurfaceFormat.setAlphaBufferSize(mWindowDecorationEnabled ? 8 : 0);
+}
+
 }
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/wayland/qwaylandshmwindow_p.h b/src/plugins/platforms/wayland/qwaylandshmwindow_p.h
index f11df5e4767..dab9e1e5350 100644
--- a/src/plugins/platforms/wayland/qwaylandshmwindow_p.h
+++ b/src/plugins/platforms/wayland/qwaylandshmwindow_p.h
@@ -29,7 +29,8 @@ public:
     ~QWaylandShmWindow() override;
 
     WindowType windowType() const override;
-    QSurfaceFormat format() const override { return QSurfaceFormat(); }
+
+    void setWindowFlags(Qt::WindowFlags flags) override;
 };
 
 }